crustal contamination in palaeogene east greenland flood basalts plumbing system evolution during continental rifting abstract palaeogene central east greenland flood basalts have sr nd and pb isotope characteristics consistent with crustal contamination of icelandic type basalts in the lower basalts of central east greenland amphibolite facies gneiss is the dominant contaminant at low stratigraphic levels whereas contamination with granulite facies gneiss prevails in the upper part of the lava succession the contamination probably occurred by partial melting of the crust and can be modelled by assimilation fractionation crystallisation processes similar contaminants have been detected in lavas from odp leg 152 off the se greenland coast although in a reverse sequence contamination in lower basalts and odp leg 152 lavas which erupted through an archaean proterozoic substrate differs from lavas in ne greenland which overly the caledonian fold belt and large mesozoic sediment deposits in the ne greenland lavas the dominant contaminant appears to be a dacitic component formed by partial melting of mesozoic sediments changes in magma supply rates from the mantle may be the determining factor for the sequence of contaminants and may also control the depth of ponding in crustal chambers the compositional variation of the least contaminated east greenland basalts suggests that melts were produced from mantle sources similar to present day iceland and north atlantic morb at the time of continental breakup but distinction between mantle sources is very complicated ree systematics indicate a maximum in initial depth of mantle melting at kangerlussuaq during formation of the east greenland flood basalts consistent with a plume being centered in that region

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

the nature and genesis of marginal cu pge au sulphide mineralisation in paleogene macrodykes of the kangerlussuaq region east greenland the kangerlussuaq region of east greenland hosts a variety of early tertiary extrusive and intrusive igneous rocks related to continental break up and the passage of the ancestral iceland plume these intrusive bodies include a number of gabbroic macrodykes two of which the miki fjord macrodyke and the newly discovered togeda macrodyke contain cu pge au sulphide mineralisation along their margins sulphides occur as disseminated interstitial blebs and rounded globules of chalcopyrite and pyrrhotite with some fe ti oxides and platinum group minerals comprising largely pd bismuthides and tellurides the globules are interpreted to have formed from fractionation of trapped droplets of an immiscible cu and pd rich sulphide melt and show geopetal indicators sulphur isotopes imply a local crustal source of s in these from pyritic sediments of the kangerlussuaq basin thus generation of these sulphide occurrences was controlled by local country rock type low ni cu and pt pd ratios also present in the platinova reefs in the skaergaard intrusion indicate that early fractionation of olivine may have depleted the magma of ni and suggest the likely presence of a large magma chamber at depth xenoliths of ni rich olivine cumulates in the miki fjord macrodyke may have been sourced from such a body the location of thus far unidentified conduit or feeder zones to the macrodykes beneath the present day surface may represent potential targets for more massive sulphide orebodies

metasomatic replacement in the skaergaard intrusion east greenland preliminary observations abstract several unusual types of replacement structures in the layered series and marginal border series of the skaergaard intrusion indicate that metasomatic changes have altered the modal proportions and in places the mineral composition of the gabbro the geometrical forms and compositional patterns of these features indicate that they result from reactive fluids moving through the rocks at high temperatures shortly after the magma had reached an advanced stage of crystallization the principal effect of metasomatism has been to produce strongly contrasting mafic and felsic rocks

crustal xenoliths in recent hawaiites from mount etna italy evidence for alkali exchanges during magma wall rock interaction abstract detailed mineralogical and geochemical systematics were carried out on crustal xenoliths the host hawaiite lavas erupted from mount etna sicily italy in 1892 1986 and 1989 as well as the flyschs from the volcano basement the xenoliths suffered morphological structural mineralogical and geochemical alteration induced by thermal and chemical exchange with the enclosing lava high temperature reactions and partial or complete melting as well as different mechanisms of elemental interdiffusion took place their exact nature depending on the type of xenolith an early and strong mobility of k rb and cs and their selective migration towards the anatectic melts the lava envelope was observed at both mineral phase and whole rock scales this is closely connected to a release of h 2 o cl s and co 2 associated with the dehydration and the decarbonation of the sediments thus the selective migration of the k rb and cs towards the enclosing lava as well as contamination of the host lava observed seems to be induced by a selective diffusion of alkalis away from the anatectic melts and especially by their selective transfer through the action of complex interstitial and chemically active fluids such processes might be connected to the strong enrichment in k rb and cs of the recent hawaiites from mount etna they might also substantiate the hypothesis that these enrichments result from selective contamination of the magma as a consequence of the percolation or circulation of a carrier fluid phase through the upper parts of the magmatic feeding system

petroleum accumulation in the deeply buried reservoirs in the northern dongying depression bohai bay basin china new insights from fluid inclusions natural gas geochemistry and 1 d basin modeling abstract the deeply buried reservoirs dbrs from the lijin shengtuo and minfeng areas in the northern dongying depression of the bohai bay basin china exhibit various petroleum types black oil gas condensates and pressure systems normal pressure overpressure with high reservoir temperatures 154 185 c the pressure volume temperature composition pvtx evolution of petroleum and the processes of petroleum accumulation were reconstructed using integrated data from fluid inclusions stable carbon isotope data of natural gas and one dimensional basin modeling to trace the petroleum accumulation histories the results suggest that 1 the gas condensates in the lijin area originated from the thermal cracking of highly mature kerogen in deeper formations two episodes of gas condensate charging which were evidenced by the trapping of non fluorescent gas condensate inclusions occurred between 29 25 5 ma and 8 6 5 0 ma with strong overpressure pressure coefficient pc 1 68 1 70 resulting in the greatest contribution to the present day gas condensate accumulation 2 the early yellow fluorescent oil charge was responsible for the present day black oil accumulation in well t764 while the late blue white oil charge together with the latest kerogen cracked gas injection resulted in the present day volatile oil accumulation in well t765 and 3 the various fluorescent colors yellow blue white and blue and the degree of bubble filling fv 2 3 72 5 of the oil inclusions in the minfeng area show a wide range of thermal maturity api gravity ranges from 30 to 50 representing the charging of black oil to gas condensates the presence of abundant blue white fluorescent oil inclusions with high grain obtaining oil inclusion goi values 35 8 usually 5 in oil reservoirs indicate that a paleo oil accumulation with an approximate api gravity of 39 40 could have occurred before 25 ma and gas from oil cracking in deeper formations was injected into the paleo oil reservoir from 2 8 ma to 0 ma resulting in the present day gas condensate oil accumulation this oil and gas accumulation model results in three oil and gas distribution zones 1 normal oil reservoirs at relatively shallow depth 2 gas condensate reservoirs that originated from the mixture of oil cracking gas with a paleo oil reservoir at intermediate depth and 3 oil cracked gas reservoirs at deeper depth the retardation of organic matter maturation and oil cracking by high overpressure could have played an important role in the distribution of different origins of gas condensate accumulations in the lijin and minfeng areas the application of oil and gas accumulation models in this study is not limited to the dongying depression and can be applied to other overpressured rift basins

geochemical comparison of reservoir solid bitumens with diverse origins abstract geochemical and petrologic comparison of solid bitumens with various origins from reservoirs in zaire canada and kazakhstan were studied to provide insight into their formation processes and their physical and chemical properties results of this study can help develop methods for treatment and removal of solid bitumen and evaluating producibility of associated hydrocarbon fluids characterization of these solid bitumens reveals a wide range in quantity and composition of extractables soluble material and in solid bitumen reflectance which indicate significant differences in formation processes hydrocarbon source and thermal maturity the zaire and kazakhstan samples represent end members of the spectrum of solid bitumens studied solid bitumens from the motoba field zaire are highly extractable and low in thermal maturity 0 2 0 3 bitumen reflectance reservoir mixing of a cretaceous lacustrine sourced oil and a tertiary marine sourced oil of different thermal maturities appears to be responsible for their formation in contrast solid bitumens from the tengiz field kazakhstan are characterized by their extremely low extractables high bitumen reflectance 1 and low atomic h c ratios

toward an understanding of disequilibrium dihedral angles in mafic rocks the median dihedral angle at clinopyroxene plagioclase plagioclase junctions in mafic rocks cpp is generally lower than equilibrium 109 plus minus 2 observation of a wide range of mafic bodies demonstrates that previous work on systematic variations of cpp is incorrect in several important respects firstly the spatial distribution of plagioclase compositional zoning demonstrates that the final geometry of three grain junctions and hence cpp is formed during solidification the igneous process sub solidus textural modification in most dolerites and gabbros previously thought to be the dominant control on cpp is insignificant cpp is governed by mass transport constraints the inhibiting effects of small pore size on crystallization and variation in relative growth rates of pyroxene and plagioclase during rapid cooling pyroxene preferentially fills wider pores while the narrower pores remain melt filled resulting in an initial value of cpp of 78 rather than 60 which would be expected if all melt filled pores were filled with pyroxene lower cooling rates create a higher initial cpp due to changes in relative growth rates of the two minerals at the nascent three grain junction low cpp associated with cuspate clinopyroxene grains at triple junctions can also be diagnostic of infiltration of previously melt free rocks by late stage evolved liquids the metasomatic process modification of cpp by sub solidus textural equilibration the metamorphic process is only important for fine grained mafic rocks such as chilled margins and intra plutonic chill zones in coarse grained gabbros from shallow crustal intrusions the metamorphic process occurs only in the centres of oikocrysts associated with rounding of chadacrysts

land plant evidence compatible with gradual not catastrophic change at the end of the cretaceous field study of the fossil and sedimentary record across the cretaceous tertiary k t boundary in wyoming and montana has been combined here with a reassessment of the published record of terrestrial palynomorphs to test recent hypotheses that a universal biotic catastrophe caused by an asteroid1 3 cometary impact4 or a supernova5 terminated the cretaceous evidence from land plants is particularly critical because plants form the base of the terrestrial food chain thus massive disruptions of the earth s vegetation by the postulated effects of a cosmic disaster blocking of solar radiation for several years by a dust cloud1 severe atmospheric heating1 4 6 7 or ionizing radiation5 would have an amplified effect on the land fauna however i report here that the geographically uneven and generally moderate levels of extinction and diversity change in the land flora together with the non synchroneity of plant and dinosaur extinctions contradict hypotheses that a catastrophe caused terrestrial extinctions

pennsylvanian coal and associated bitumen at johnson mills shepody bay new brunswick canada abstract pennsylvanian fluviatile sandstones at johnson mills new brunswick host fossil logs preserved as a result of the paragenetic succession pyritization carbonatization carbonization and overlapping bitumenization carbonatization is the dominant process the coalified material is all overmature as reflected by temperature of maximum pyrolysis tmax in a range of 460 464 c veinlets of once liquid now solid bitumen extend outward from the logs into the surrounding sandstones for several meters present in the bitumen are relict coal macerals that contribute to a microscopic distinctly structured coaly appearance of the material reflectance measurements of coal range from romax 0 78 to romin 0 61 two distinct populations of bitumens are recognized romax 0 78 to romin 0 65 for the main population romax 0 60 to romin 0 48 for the second population transmitted and reflected light microscopy long count energy dispersive spectroscopy eds and rock eval analysis indicate that bitumen was derived from the logs as a result of late stage diagenesis exsudatinite like material is the probable precursor of the bitumen thermal maturity of the bitumen increases directly with inferred migration distance from the logs across the spectrum solid bitumen closest to the logs and within the oil window is least mature tmax 449 c and bitumen furthest from the logs is most mature with tmax 493 c this phenomenon results from differences in the chemistry of the derivative bitumen which is relatively more aliphatic and nso enriched close to the log source and more aromatic distally these differences in bitumen composition may have arisen as a consequence respectively of pre gas and post gas generating conditions

testing the terrestrial δ13c cretaceous paleogene k pg chemostratigraphic marker abstract multiple 1 13 c isotopic excursions measured across the cretaceous paleogene k pg boundary in an iridium bearing stratigraphic section from mud buttes north dakota usa fail to demonstrate an unambiguous chemostratigraphic signal for the extinction results of two sample kolmogorov smirnov tests using 13 c records for the mud buttes section as well as five other published k pg sections from montana north dakota wyoming and canada all of which report a 1 0 to 2 8 chemostratigraphic marker at or just above the extinction demonstrate that it may not be possible to distinguish a statistically meaningful isotopic shift to lower 13 c values at the boundary in the context of background variations carbon isotopes as terrestrial chemostratigraphic markers of the k pg extinction boundary are thus of limited utility

the kraemer island macrodyke east greenland solidification of a flood basalt conduit the kraemer island macrodyke that is exclusively exposed on kraemer island about 7 km west of the skaergaard intrusion belongs to a regional dyke swarm termed the skaergaard like dykes or fg 1 dykes weakly modally layered olivine gabbros dominate the exposed parts of the intrusion that has a width of 650 m to 1000 m plagioclase core an 68 2 and ca rich pyroxene core mg no 79 1 grains are normally zoned whereas olivine grains fo50 65 are homogeneous calculated mineral magma equilibria based on experimentally determined mg fe magma olivine and magma clinopyroxene partition coeffi cients suggest that the observed olivine and clinopyroxene compositions in the gabbros cannot have formed from a common parental magma the unzoned nature of olivine grains and their iron rich com positions relative to clinopyroxene suggest post cumulus mg fe exchange between olivine and interstitial melt a gabbroic pegmatite is developed in the centre of the intrusion along its entire exposed 5 km strike length here mineral zonation is limited and compositions are similar to rims of cumulus minerals in the enveloping olivine gabbros the pegmatite could therefore represent interstitial melt mobilized from gab broic cumulates that later accumulated and crystallized at its present stratigraphic location cumulus olivines in the gabbros are close to equilibrium with ca rich pyroxene in the pegmatite this is interpreted as reflecting interstitial melt mobility during the late stages of solidification of the macrodyke chilled margins are well preserved at the intrusion margins and are rich in fe 14 15 3 feo tot ti 3 3 3 tio2 and light rare earth elements la sm n 1 2 1 3 similar to magmas well represented in the overly ing sequence of contemporaneous high ti series flood basalts it is therefore likely that extensive wall rock melting adjacent to the macrodyke reflects continuous feeding of the overlying flood basalts through the kraemer island macrodyke

optical characteristics of amorphous kerogens and the hydrocarbon generating potential of source rocks abstract four recurring types of amorphous kerogen are optically identified in petroleum source rock samples and are related to hydrocarbon generating potential defined here as geochemically interpreted oil prone or gas prone at this time a genetic classification is not possible the different amorphous kerogen types are distinguished on the basis of microscopic textural differences type a chunky compact masses with mottled network or weak polygonal textures type b very small dense elongate oval or rounded individual grains type c clumpswith granular fragmented or globular textures type d thin platy or rectangular individual grains geochemistry defined oil prone samples generally contain types a and or d separately or combined geochemically defined gas prone samples rarely contain type a and vary in amounts of types b c and or d the samples in this study contain dominantly one of the four types of amorphous kerogen so the geochemical analyses of the whole rock or bulk concentrated kerogen samples are assumed to be analyses of the dominant amorphous type the samples were chemically analyzed by several techniques to determine the oil or gas generating potential the establishment of relations between specific optical and chemical properties of kerogen types can make visual kerogen analyses more meaningful in predicting the hydrocarbon generation potential of source rocks

geochemical correlation of pyrobitumen fills with host mid cretaceous black flysch group basque cantabrian basin western pyrenees abstract abundant syndepositional pyrobitumen fills occur within albian hydrothermal vent carbonates of the organic rich black flysch group in the basque cantabrian basin indicating that these carbonates were charged with oil during albian times a carbon isotopic study of pyrobitumens and samples of candidate oil generating rocks jurassic and albian host rock units as well as carboniferous sourced condensate was undertaken to test an albian source hypothesis for the pyrobitumens on the basis of similar isotopic ratio values the pyrobitumens show a strong positive correlation with the host black flysch group this is supported by stahl type curves and a sofer plot which show that the pyrobitumens best match the host albian deposits whereas the jurassic source rock and the carboniferous sourced condensate plot separately this new albian pyrobitumen source correlation demonstrates the existence of an oil generating rock unrecognised till now in the basque cantabrian basin the mid cretaceous black flysch group

organic facies and palynofacies nomenclature classification and applicability for petroleum source rock evaluation abstract the basic aim of the investigation presented in this paper was to determine all relevant petrographical and geochemical characteristics of organic facies and their correlation with the lithological composition sedimentation conditions and paleoenvironments application of geological and geochemical methods gives new insight into problems concerning determination of the potential and efficiency of petroleum source rocks in making the qualitative and quantitative analyses of organic matter in this study various analytical methods were used whole rock samples kerogen concentrates transmitted and reflected normal and fluorescent light the type of organic facies was used as a criterion for the identification accumulation and transformation of the organic matter paleobotanical studies of organic facies and palynofacies were used to identify types of vegetation and draw conclusions concerning the sedimentary environment various types of organic facies and palynofacies were classified in relation to the origin of the organic matter all sedimentary organic constituents of continental huminite vitrinite inertinite cuticle wood fragments tracheids spores and pollen and marine mostly autochthonous dinocysts algae foraminifera test linings acritarchs and amorphous organic matter origin have been grouped according to different classification systems a summary of these classifications is proposed with remarks on approximate corresponding coal macerals and selected kerogen types

geochemical characterization of solid bitumen in the chesterian mississippian sandstone reservoir of the hitch field southwest kansas solid bitumen was identified within the mississippian chester sandstone reservoir in the hitch field southwest kansas the adjacent etzold field has similar reservoir properties but lacks solid bitumen although the hitch and etzold fields were thought to be in pressure communication and have common source rocks hitch and etzold crude oils and core extracts were characterized geochemically to gain a better understanding of the reservoir filling history and geological and geochemical controls on solid bitumen formation in the hitch reservoir based on a variety of geochemical characteristics we propose that the hitch and etzold oils are mixtures derived from ordovician and late devonian early mississippian woodford shale source rocks the solid bitumen in the hitch reservoir probably results from mixing of oils having different geochemical compositions which filled the reservoir over an extended period no evidence of severe biodegradation or thermal alteration is observed a reservoir filling scenario is proposed in an effort to explain why the hitch oils are geochemically more heterogeneous than etzold oils furthermore gas de asphalting and regional pressure drops as a result of post laramide orogeny may have contributed to a phase change in the reservoir fluid and deposition of solid materials by disturbance of thermodynamic equilibrium the major significance of this study is related to improving our knowledge on the occurrence of the presence of solid bitumen in reservoirs that can introduce barriers into the reservoir complicating waterflood operations and leading to erroneous oil in place calculations and subsequently lower than expected oil recovery

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

carbon and hydrogen stable isotope variations in kerogen during laboratory simulated thermal maturation carbon and hydrogen stable isotope measurements on sapropelic and humic kerogen isolated from laboratory heated sediments reveal several isotopic trends an initial depletion of 13c and d 2h or deuterium in kerogen isolated from the heated sapropelic sediment appears to be the result of isotopic heterogeneity interaction with soluble organic matter and or volatilization of a heat labile fraction of the protokerogen during the main isotopic trend the sapropelic kerogen becomes enriched in 13c and d by about 5 and 50 ppt parts per thousand respectively theoretical calculations based on a rayleigh fractionation process suggest that this trend is largely controlled by the generation of isotopically light methane directly from the ker gen this argument also applies to the main hydrogen isotopic trend for the humic kerogen which becomes enriched in d by about 90 ppt the main 13c trend for the humic kerogen however results in a maximum enrichment in 13c of only about 1 6 ppt and appears to be largely controlled by factors other than methane a final depletion trend in 13c and d occurs for the sapropelic kerogen at very high temperatures this may be due to a reduced isotopic fractionation at higher temperatures or to the indirect generation of methane from kerogen through a liquid intermediate which is subsequently coked to pyrobitumen

albanerpetontid amphibians from the late cretaceous santonian of iharkut hungary with remarks on regional differences in late cretaceous laurasian amphibian assemblages since its discovery in 2000 the iharkut fossil locality in the upper cretaceous santonian csehbanya formation of western hungary has yielded a taxonomically diverse assemblage of terrestrial and freshwater vertebrates that continue to provide insights into the diversity paleobiogeography and paleoecology of late cretaceous vertebrates in europe albanerpetontidae an extinct group of superficially salamander like amphibians that were widespread across laurasia during the latter part of the mesozoic are represented at iharkut by 16 fragmentary jaws here we describe and figure these specimens as albanerpetontidae genus and species indeterminate based on the age of the iharkut locality several premaxillary features the known distribution late early cretaceous late pliocene of the type genus albanerpeton and an unusually large dentary specimen we suggest that the iharkut albanerpetontid may pertain to a previously unrecognized species of albanerpeton but verification of that must await the re

late maastrichtian continental vertebrates from southwestern france correlation with marine fauna abstract the cassagnau locality marignac laspeyres haute garonne department has yielded the richest vertebrate assemblage of late maastrichtian age in western europe numerous bones can be referred to various fishes amphibians chelonians squamates crocodiles dinosaurs and birds some of which constitute the first late maastrichtian occurrences in europe a large varanoid lizard a longirostrine crocodile an enantiornithine bird or in southern france a titanosaurid dinosaur the latter discovery shows that at least five dinosaur families were represented in the late maastrichtian of western europe as for other localities of the french petites pyrenees the age of the cassagnau locality can be directly constrained by biostratigraphical and biochronological evidence based on associated marine and continental microfauna and microflora therefore the assemblages from these localities can be considered as reference assemblages for the continental late maastrichtian localities of southern europe the age of which has been much disputed

dinosaur abundance was not declining in a 3 m gap at the top of the hell creek formation montana and north dakota comment and reply comment the study of dinosaur abundance in the hell creek formation by sheehan et al 2000 1 raises three points that require comment additionally some of their history of the 3 m gap requires emendation as the authors correctly state in the late 1970s and early 1980s various workers observed

modeling free gas content of the lower paleozoic shales in the weiyuan area of the sichuan basin china abstract two sets of lower paleozoic organic rich shales develop well in the weiyuan area of the sichuan basin the lower cambrian jiulaodong shale and the lower silurian longmaxi shale the weiyuan area underwent a strong subsidence during the triassic to early cretaceous and followed by an extensive uplifting and erosion after the late cretaceous this has brought about great changes to the temperature and pressure conditions of the shales which is vitally important for the accumulation and preservation of shale gas based on the burial and thermal history averaged toc and porosity data geological and geochemical models for the two sets of shales were established within each of the shale units gas generation was modeled and the evolution of the free gas content was calculated using the pvtsim software results show that the free gas content in the lower cambrian and lower silurian shales in the studied area reached the maxima of 1 98 2 93 m3 t and 3 29 4 91 m3 t respectively under a pressure coefficient of 1 0 2 0 at their maximum burial subsequently the free gas content continuously decreased as the shale was uplifted at present the free gas content in the two sets of shales is 1 52 2 43 m3 t and 1 94 3 42 m3 t respectively under a current pressure coefficient of 1 0 2 0 the results are roughly coincident with the gas content data obtained from in situ measurements in the weiyuan area we proposed that the lower cambrian and lower silurian shales have a shale gas potential even though they have experienced a strong uplifting

oxygen isotopes from biogenic apatites suggest widespread endothermy in cretaceous dinosaurs the much debated question of dinosaur thermophysiology has not yet been conclusively solved despite numerous attempts we used the temperature dependent oxygen isotope fractionation between vertebrate body water 18obody water and phosphatic tissues 18op to compare the thermophysiology of dinosaurs with that of non dinosaurian ectothermic reptiles present day 18op values of vertebrate apatites show that ectotherms have higher 18op values than endotherms at high latitudes due to their lower body temperature and conversely lower 18op values than endotherms at low latitudes using a data set of 80 new and 49 published 18op values we observed similar and systematic differences in 18op values 18o between four groups of cretaceous dinosaurs theropods sauropods ornithopods and ceratopsians and associated fresh water crocodiles and turtles expressed in terms of body temperatures tb these 18o values indicate that dinosaurs maintained rather constant tb in the range of endotherms whatever ambient temperatures were this implies that high metabolic rates were widespread among cretaceous dinosaurs belonging to widely different taxonomic groups and suggest that endothermy may be a synapomorphy of dinosaurs or may have been acquired convergently in the studied taxa

structural model of the central longmen shan thrusts using seismic reflection profiles implications for the sediments and deformations since the mesozoic abstract the structural setting and deformation history are very important aspects of understanding the frequent earthquakes and assessing the hazards in this paper we interpret two new seismic profiles that were collected after the wenchuan mw7 9 earthquakes occurred on may 2008 our interpretation has integrated four wells three seismic profiles and the surface geology to reveal structural characteristics of the central longmen shan thrust the drilled wells reveal that there are two detachments within the upper triassic and the lower triassic at the longmen shan thrusts the shallow detachment fault transferred its slip to the basin and made another deformation inner the sichuan basin between the shallow detachments many faults developed and the major structures at the thrust front have formed as structural wedges both the drilled wells and seismic interpretation show the upper triassic repeated in the depth the shortening at the central longmen shan thrust is approximately 30 37 according to geological survey and the seismic interpretation the foreland basin was developed during the late triassic and the angular unconformity between the lower jurassic and the upper triassic at the longmen shan front several different tectonic events can be identified since the mesozoic which indicated that the longmen shan has a complex evolution history in our model the major beichuan fault f2 and the pengguan fault f3 at the central longmen shan dip steeply near the surface but are more gentle dipping at depth both of the shallow thrusting and the basement shortening made contribution to the rapid uplift of the longmen shan during the cenozoic the co seismic ruptured fault is like a branchy fault that developed on the major fault system the wenchuan mw7 9 earthquake and the lushan mw6 7 earthquake may be related to the reaction of the basement structures

late cretaceous maastrichtian chondrichthyes and osteichthyes from northeastern iberia abstract intensive sampling for vertebrate microfossils has yielded abundant fish remains in the maastrichtian units of the tremp formation southern pyrenees catalonia spain samples were taken from eight new sites representing different palaeoenvironments including coastal wetlands and floodplains in order to assess the fish diversity and to gain a better understanding of the last dinosaur dominated ecosystems of northeastern spain the results suggest that a diverse ichthyofauna inhabited these transitional to inland fluvial settings throughout the maastrichtian comprising both marine and freshwater taxa three different chondrichthyans eight basal neopterygians and at least seven teleostean species were found the latter being more diverse than in other maastrichtian localities in europe fossil evidence from the studied late maastrichtian assemblages suggests that teleosteans were present in all the trophic guilds in addition the oldest records for osteoglossids and perciforms in europe as well as for cypriniforms worldwide are reported here the findings from the southern pyrenees also reveal ichthyofaunal turnover during the late cretaceous with holosteans being replaced by teleosteans moreover maastrichtian ichthyofaunas from the southern pyrenees show asian and north american biogeographical affinities

integrated stratigraphy from the vallcebre basin southeastern pyrenees spain new insights on the continental cretaceous tertiary transition in southwest europe abstract an integrated sedimentological magnetostratigraphic and paleontological study of the vallcebre section south eastern pyrenees spain is carried out in order to define and portray the transition from the cretaceous to the tertiary in a continental setting a robust magnetostratigraphy is correlated to the standard polarity scale in light of known biochronological constraints charophyte marine invertebrates eggshells and other dinosaur remains our results show that this section is among the thickest stratigraphic records for the continental maastrichtian in the old world sedimentology indicates a progressive regression from marine through lagoonal to entirely continental environments the section is dominated by mudstones deposited under low energy conditions exceptionally a basin wide regression maximum is recorded some time before the cretaceous tertiary boundary k t this regression maximum is marked by the input of coarse grained alluvial sediments that record a dramatic change in the landscape quiet mud plains changed to sandy floodplains deposited by high energy currents after a period of renewed quiescence following the regression maximum a cenozoic flooding took place such terminal cretaceous sequence of events has been recorded in shorter sections in several other basins from southwestern europe this energetic sediment input suggests that some time before the k t event a sudden paleoenvironmental reorganization took place in the continental basins of south western europe

evidence from paleosols for ecosystem changes across the cretaceous tertiary boundary in eastern montana ancient soils paleosols of the latest cretaceous hell creek formation are mildly calcareous have clayey subsurface bt horizons and exhibit abundant large root traces as is typical of forested soils in subhumid climates the fact that some of the paleosols are capped by thin impure coals is evidence for seasonally dry swamps the paleosol evidence thus supports published reconstructions based on fossil leaves pollen and vertebrates that this area was subtropical seasonally dry subhumid and forested mainly by angiosperms paleosols within the earliest tertiary paleocene tullock formation have thicker coaly surface o and a horizons and are more drab colored and less calcareous than paleosols of the hell creek formation these features are indications of waterlogging and of a humid climate large root traces and clayey subsurface bt horizons are evidence of swamp woodland and forest inferred base level and paleoclimate are compatible with evidence from fossil leaves and pollen that indicates more abundant deciduous early successional angiosperms and swamp conifers compared to those of late cretaceous time most of the paleosols have drab munsell hues and can be expected to preserve a reliable fossil record of pollen and other plant remains the carbonate content of the paleosols declines toward the top of the hell creek formation and the uppermost 3 m of the formation is noncalcareous because of this the decline in diversity and abundance of bone over this interval is interpreted as a taphonomic artifact evidence from paleosols supports paleobotani cal evidence for catastrophic change in ecosystems at the cretaceous tertiary boundary

source rock evaluation by pyrolysis gas chromatography a pyrolysis gas chromatography system has been developed for the rapid evaluation of potential source rocks for the determination of organic richness and maturation this system uses the pyrolysis methods previously described however the determination of hydrocarbon production type and the identification of contamination by migrated hydrocarbons or drilling additives are accomplished by gas chromatographic gc analysis of the thermal extracts and pyrolysis products of rock samples or isolated kerogens the production type is recognized either qualitatively by gc fingerprint traces or quantitatively by hydrocarbon composition c1 to c6 c6 to c11 c11 from the kerogen peak ii pyrolysate oil prone erogens are recognized by gc traces with a full spectrum of c1 to c28 hydrocarbons or by high concentrations of c11 compounds in contrast gas prone kerogens are characterized by the predominance of light hydrocarbons from c1 to c4 and higher contributions of aromatic compounds mixed type production is intermediate in character between the two contaminants are identified from the gc analysis of the thermally extractable material in peak i possible mineral organic matter reactions during sample heating make interpreting data from whole rock samples more difficult

the study on the source of the oil seeps and bitumens in the tianjingshan structure of the northern longmen mountain structure of sichuan basin china abstract the tianjingshan structure of the northern longmen mountain is located in the north of the sichuan province china two primary source rocks are present in this region the overmature infracambrian lower cambrian source rocks and the mature upper permian source rocks oil seeps and solid bitumens occur extensively in the mesozoic and paleozoic marine strata indicating good exploration prospects in this area however oil to source correlation in the tianjingshan structure is difficult due to both high maturity of the lower cambrian source rocks and severe biodegradation of oil seeps and bitumens in this work one oil seep from the permian qixia formation and two severely degraded bitumens from the cambrian strata in the tianjingshan structure were correlated with their potential source rocks hydropyrolysis was used to release biomarkers bound to kerogen of the overmature lower cambrian source rock the released biomarkers were used for the oil to source correlation together with those indexes resistant to thermal degradation and biodegradation based on the geochemical data and the petroleum geological settings of the area it can be inferred that the cambrian ordovician and silurian bitumens with light bulk isotopic values commonly 13 c

the diversity of sauropod dinosaurs and their first taxonomic succession from the latest cretaceous of southwestern europe clues to demise and extinction article i nfo southwestern europe is a key setting to evaluate the diversity of non avian dinosaurs before the end of the cretaceous below the k pg boundary the ancient ibero armorican island encompassing the current regions of north east iberia and south france provides a substantial record of sauropod fossils the study of multiple sauropod femora from localities where upper campanian to uppermost maastrichtian successions are both exposed together with the integration of the information gathered from previously known localities has allowed the biodiversity of sauropods to be reassessed within a precise and clear chronostratigraphic framework from the studied sample several titanosaur forms have been distin guished including a gracile and small sized titanosaur lirainosaurus astibiae a robust medium sized titanosaur ampelosaurus atacis a gracile medium sized titanosaur atsinganosaurus velauciensis and five other indeterminate but distinct titanosaurs which span the late campanian through the entire maastrichtian the youngest of these occurs in the uppermost part of palaeomagnetic chron c30n in the latest maastrichtian 0 4 1m a before the k pg boundary representing the youngest sauropod yet doc umented in eurasia the pattern of diversity on the ibero armorican island rules out a decline in sauropod diversity at the very end of the cretaceous as with other regions during the late cretaceous the abundance and quality of the sauropod fossil record is probably influenced by multiple biases sampling ecological and environmental

origin properties and implications of solid bitumen in source rock reservoirs a review abstract this paper reviews the significance of solid bitumen with emphasis on source rock reservoirs we discuss difficulties and discrepancies with terminology especially those terms related to the origin of solid bitumen and its physical and chemical properties various definitions of solid bitumen have their own justifications and can be used provided there is clarity about which defining criteria are being considered difficulties in conforming to chemical solubility or origin related definitions lead us to suggest adapting the reflectance of solid hydrocarbon as a practical choice for placing the boundary between solid bitumen and pyrobitumen and 1 50 is proposed as the boundary value it has to be noted that this boundary may be shifted down to 1 3 for sulfur rich kerogen recently much progress has been made by combining imaging and physical adsorption techniques in porosity studies and so the porosity of solid bitumen is given special emphasis comparing pore characteristics obtained from sem versus those generated by gas adsorption mercury intrusion or neutron scattering techniques indicates that the sem pore inventory fails to account for the smallest pores we review the implications of the abundance of solid bitumen on reservoir quality porosity permeability and producibility based on examples of selected sequences one of the difficulties in predicting the influence of solid bitumen bearing horizons on reservoir quality arises from the problems with detecting organic phases using various logging techniques the use of specialized techniques such as nmr logging that allows two dimensional t1 and t2 measurements should be expanded and other potential techniques need to be further researched and tested certain aspects of the properties of solid bitumen that are not as well understood such as its hydrocarbon generation potential or its role in hydrocarbon migration are also discussed with the aim of identifying further research that could lead to a better understanding of the role that solid bitumen plays in unconventional reservoirs

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

the effect of maturation on the isotopic composition of fossil fuels abstract few measurements of the d h ratios in liquid and solid fossil fuels have been made additional isotopic data are reported here in the form of d h and 13 c 12 c ratios for crude oils and brown coals which occur together in the bass strait region of australia studies of petrographic fractions of these coals and of the changes in the isotopic composition of coals and coal extracts with increasing maturity show that the original d h ratios characteristic of contributing plant materials are more readily erased and homogenized during early diagenesis than the corresponding 13 c 12 c ratios

the skaergaard layered series part vii sr and nd isotopes the initial isotopic ratios of strontium and neodymium in the skaergaard layered series vary both vertically and laterally on every scale from the intrusion as a whole down to coexisting minerals in a single rock the magma that filled the skaergaard chamber was contaminated to various degrees with the metamorphic rocks through which it rose and was never completely homogenized after being intruded the contamination was most pronounced in contact zones and aureoles around rare xenoliths the greater concentrations of lithophile trace elements in the upper border series was previously attributed to assimilation of buoyant fragments of gneiss that collected under the roof but most of the rocks of the upper border series are isotopically indistinguishablefromthoseofthelayeredseries itisdoubtful therefore that this part of the intrusion assimilated much more of the metamorphic basement than did the rest of the magma similarly the marked increase in the concentrations of excluded elements in the upper part of the layered series is not matched by a change in the isotopic character of the rocks and cannot be attributed to a later influx of new magma analyses of minerals separated from rocks with exceptionally mafic or felsic modal compositions revealed marked inhomogeneities in the isotopic compositions of their constituent minerals for example coexisting plagioclase and pyroxene from closely associated anorthosites and pyroxenites have very different initial isotopic ratios of both strontium and neodymium the same is true of mafic and felsic layers in modally graded gabbros these differences are unrelated to the low temperature alteration shown by oxygenisotopes they must have been introduced when the original gabbro was largely crystallized and underwent local metasomatic replacement by nearly mono mineralic mafic and felsic assemblages

generation and polybaric differentiation of east greenland early tertiary flood basalts major element trace element isotope and petrographic studies of magma diverentiation mantle melting the basal volcanics in the kangerdlugssuaq fjord region of the east greenland margin provide constraints on the generation and subsequent diverentiation and contamination histories of magmas during the early stage of continental rifting creating the north atlantic ocean basin most primitive lavas of the succession are introduction shown to have accumulated olivine corrections for crystal ac the distinctive geochemical features of continental flood cumulation yield estimates for erupted primitive liquids with mgo basalts cfbs are strongly controlled by the composition contents between 9 and 13 wt the occurrence of suspended and structure of the continental lithosphere and underfo88 olivine phenocrysts further requires the existence of parental lying mantle significant controversy remains concerning magmas with mgo contents up to 17 wt and feo contents up the balance of contributions from the lithosphere and to 14 wt quantitative modeling of fractionation indicates the mantle and the mechanisms by which the various that kangerdlugssuaq magmas primarily diverentiated at moderate source components contribute to basalt petrogenesis pressures 8 kbar to form dunitic and wehrlitic cumulates at how are basalt compositions influenced by generation depths of 25 km evolved east greenland flood basalts from the in anomalous regions in the deep mantle plumes by scoresby sund region record a more complex fractionation history interaction between rising magmas and the continental involving olivine clinopyroxene fractionation in the lower crust lithospheric mantle and by contamination with conas found for the lower basalts followed by olivine plagioclase tinental crust how are the diverentiation con clinopyroxene fractionation at shallow crustal levels cor tamination magma mixing and storage histories of cfbs relations between sio2 incompatible elements and sr nd isotopic controlled by the structure of the continental lithosphere ratios for the lower basalts are consistent with bulk assimilation and how do the thermal and chemical features of the of up to 15 20 archean leucogneiss with unradiogenic sr and mantle and the extensional history of the continental nd isotopic ratios characteristic of lewisian type lower crust lithosphere avect mantle melting and compositions of comparisons between inferred magma types for lower basalts and primary liquids estimated primary liquids from elsewhere in the north atlantic these questions are best addressed in the context of show complex relationships among feo mgo tio2 contents a geologically and geochemically well constrained cfb and cao al2o3 ratios that relate to regional and temporal changes province such as the north atlantic tertiary province in mantle temperatures lithospheric thickness and involvement of separation of east greenland from northern europe in at least two end member mantle sources we postulate that the the early tertiary at 60 myr ago was accompanied by lower basalts of east greenland were derived from iron poor voluminous volcanic activity the blosseville coast of mantle depleted by prior melt extraction and distinct from morb east greenland extending from kangerdlugssuaq fjord source mantle that was enriched in tio2 and lrees by a to scoresby sund fig 1 contains spectacularly exposed metasomatic event shortly before early tertiary magmatism we sections of lavas these sections begin at the basal contact associate this depleted mantle source with the ancestral iceland of the lavas with underlying cretaceous tertiary sediments and archean basement and continue to the plume anomaly

geochemistry of crude oils from eastern indonesia high resolution geochemistry shows genetic relationships among 27 crude oils from eastern indonesia and suggests the ages and paleoenvironments of their source rocks oils inferred to originate from tertiary and triassic jurassic source rocks in the study occur north and south of 2is latitude respectively twenty oils mainly from irian jaya and sulawesi originated from tertiary marine marlstone source rocks that contained type ii iii kerogen deposited under suboxic conditions probably the upper miocene klasafet formation these low sulfur oils show high oleanane c26 24 nordia cholestane and pristane phytane ratios and 13c rich carbon isotope compositions high oleanane and 24 nordiacholestane ratios are diagnostic of tertiary oils and source rocks these oils account for about 16 of the estimated ultimate recoverable reserves in eastern indonesia

orogenic gold mineralisation hosted by archaean basement rocks at sortekap kangerlussuaq area east greenland a gold bearing quartz vein system has been identified in archaean basement rocks at sortekap in the kangerlussuaq region of east greenland 35 km north northeast of the skaergaard intrusion this constitutes the first recorded occurrence of au mineralisation in the metamorphic basement rocks of east greenland the mineralisation can be classified as orogenic style quartz vein hosted au mineralisation two vein types have been identified based on their alteration styles and the presence of au mineralisation mineralised type 1 veins occur within sheared supracrustal units and are hosted by garnet bearing amphibolites with associated felsic and ultramafic intrusions gold is present as native au and au rich electrum together with arsenopyrite and minor pyrite and chalcopyrite in thin alteration selvages in the immediate wall rocks the alteration assemblage of actinolite clinozoisite muscovite titanite scheelite arsenopyrite pyrite is considered to be a greenschist facies assemblage the timing of mineralisation is therefore interpreted as being later and separate event to the peak amphibolite facies metamorphism of the host rocks type 2 quartz veins are barren of mineralisation lack significant alteration of the wall rocks and are considered to be later stage fluid inclusion microthermometry of the quartz reveals three separate fluids including a high temperature th 300 350 c h2o co2 ch4 fluid present only in type 1 veins that in interpreted to be responsible for the main stage of au deposition and sulphidic wall rock alteration it is likely that the carbonic fluids were actually trapped at temperatures closer to 400 c two other fluids were identified within both vein types which comprise low temperature 100 200 c brines with salinities of 13 25 wt eq nacl and at least one generation of low salinity aqueous fluids the sources and timings of the secondary fluids are currently equivocal but they may be related to the emplacement of paleogene mafic intrusions the identification of this occurrence of orogenic style au mineralisation has implications for exploration in the underexplored area of east greenland between 62 and 69 n where other similar supracrustal units are known to be present

the origin of 4 methyl steranes and pregnanes from tertiary strata in the qaidam basin china abstract a geochemical study of oils and source rocks in tertiary saline lake facies from the qaidam basin of china demonstrates that pregnanes are mainly derived from the thermal degradation of organic matter in source rocks synchronous with hydrocarbon genesis whereas 4 methyl steranes may principally be a product of microbial activity during diagenesis

relationships between hydrocarbon evolution and the geochemistry of solid bitumen in the guanwushan formation nw sichuan basin abstract recently the devonian guanwushan formation in the northwestern sichuan basin gained industrial attention when solid bitumen was discovered in reservoirs and outcrops this discovery initiated the exploration and development of the devonian natural gas devonian in the northwestern sichuan basin is a new stratum for the exploration and development of paleozoic marine natural gas in sichuan basin however the unclear recognition on the genesis the sources and the hydrocarbon evolution history of solid bitumen and natural gas seriously restricted further exploration and development based on the solid bitumen reflectance carbon isotopes saturated hydrocarbon chromatography and solvent extract bitumen biomarkers combined with the component and carbon isotopes of natural gas comprehensive analyses have been performed on the origin of the solid bitumen and the accumulation and evolution of the natural gases the results showed that the outcrop solid bitumen is derived from biodegraded oil from the lower cambrian source rocks and is characterised by low bitumen reflectance low saturated aromatic hydrocarbon ratios seriously damaged normal alkanes and severe migration of the gas chromatographic baseline the reservoir bitumen formed through thermal cracking of oil from lower cambrian and lower permian source rocks and is characterised by high bitumen reflectance high saturated aromatic hydrocarbons and complete normal alkanes the differences of tectonic evolution take control of the two different genesis bitumen the longmen mountain strata in the northwestern sichuan basin were uplifted sharply after the jurassic and the early generated crude oil was biodegraded during uplifting and formed the outcrop bitumen however strata in well shuangtan 3 st3 continued to subside and the paleo reservoir thermal cracked during deep burial into dry gas and heavy components gathered to form reservoir bitumen revealing the devonian hydrocarbon evolution in sichuan basin is of highly significance and is meaningful to guide further researches on the gas source correlation of natural from paleo strata it is of great significance to reveal the devonian hydrocarbon evolution in sichuan basin and to guide further researches on the gas source correlation of natural gas from paleo strata

strontium isotope systematics for plagioclase of the skaergaard intrusion east greenland a window to crustal assimilation differentiation and magma dynamics author s hagen peter g tegner c lesher ce abstract 2019 geological society of america we present in situ laser ablation multicollector inductively coupled plasma mass spectrometry sr isotope data for plagioclase from a reference stratigraphic profile of the entire layered series and upper border series of the skaergaard intrusion east greenland plagioclase sr isotope compositions and anorthite contents vary systematically from the margins of the intrusion inwards the lowest 87sr 86sri calculated at 56 ma values 0 7041 occur near the base and top of the intrusion and systematically increase over several lithostratigraphic zones to a value of 0 7044 which is uniform throughout the middle 2000 m of intrusion across this same profile anorthite content of plagioclase varies smoothly from an65 70 at the base and top to an25 approaching the purported sandwich horizon plagioclase near the roof and proximal to rafts of partially assimilated basement gneiss are markedly more radiogenic 87sr 86sri up to 0 7046 we explain the stratigraphic relationships by progressive contamination of the magma during early stages of differentiation by basement gneiss rafts entrained during emplacement and accumulated near the top of the chamber contamination was transient ceasing once the entrained gneiss was consumed or isolated from the main magma reservoir as the solidification front advanced modeling of fractionation assimilation processes accounts for the observed isotopic trends with only a few percent assimilation relative to the original magma mass the record of contamination revealed by sr in plagioclase supports the view that the bulk of the skaergaard intrusion formed by closed system differentiation with only minor in situ contamination and no magma recharge comparing plagioclase and bulk rock sr suggests that the latter may have witnessed late stage metasomatic overprinting of phases other than plagioclase

discovery of oil bitumen co existing with solid bitumen in the lower cambrian longwangmiao giant gas reservoir sichuan basin southwestern china implications for hydrocarbon accumulation process abstract natural gas in the recently discovered lower cambrian longwangmiao giant gas reservoir of the sichuan basin in southwestern china has been considered to be from oil cracking and sourced from the underlying lower cambrian qiongzhusi shales similar to the underlying neoproterozoic dengying giant gas reservoir however geological considerations and differences in geochemistry between the longwangmiao and dengying gases bitumens imply different scenarios organic petrology geochemistry and trace element analyses of widely occurring bitumen were conducted to evaluate this hypothesis results show the coexistence of solid bitumen and oil bitumen in this reservoir for the first time which implies a new hydrocarbon accumulation process and associated exploration strategies the two types of bitumen were termed type a solid bitumen and type b oil bitumen which were sourced from the lower cambrian qiongzhusi formation shale and the lower silurian longmaxi shale respectively the type a solid bitumen shows little fluorescence and its color under plane polarized light is almost black this indicates that the type a solid bitumen is likely of high maturity it typically occurs in dissolution pores and accounts for approximately 90 of all bitumen in the reservoir in contrast the type b oil bitumen is brown black in color under plane polarized light and yellow green under fluorescence light indicating that it is mature it occurs in the residual spaces of the solid bitumen and represents approximately 10 of the total bitumen content this suggests that type a bitumen charged the reservoir earlier than did the type b bitumen during the indosinian epoch of the triassic oil generated from the mature qiongzhusi formation migrated into the longwangmiao and dengying reservoirs following this the dengying reservoir reached the temperature threshold for oil cracking since the late cretaceous and it is suggested that oil could have started to crack to gas which is the critical moment for the gas formation however the longwangmiao oils had not been cracked at this stage because the reservoir temperature had not reached the threshold later during the himalayan epoch the gas in the dengying reservoir as well as some kerogen cracking gas from the qiongzhusi shales migrated into the longwangmiao reservoir along faults gas gravity drainage and phase separation took place in the longwangmiao reservoir forming the type a solid bitumen and giant gas accumulation later oil generated from the longmaxi shales migrated into the longwangmiao reservoir forming the type b oil bitumen the case here is an example of a multi stage oil and gas accumulation future exploration targets should include middle upper cambrian reservoir rocks

theropod teeth from the basalmost cretaceous of anoual morocco and their palaeobiogeographical significance the theropod teeth from the berriasian early cretaceous site of anoual n morocco are described the assemblage is important in that it comes from one of the very few dinosaur sites of this age globally and the only one for the whole of gondwana the theropod teeth from anoual are morphologically diverse most of the material possibly belongs to the clade dromaeosauridae which would be an early occurrence for this taxon the palaeogeographic position of anoual enables it to provide data on the dispersal events that affected terrestrial faunas during mesozoic times a laurasian influence is evidenced by the presence of velociraptorinae and on the whole the theropod fauna from anoual provides support for the existence of a trans tethyan passage allowing terrestrial faunal interchanges during late jurassic and or earliest cretaceous times additionally anoual records the existence of diminutive theropods however it cannot yet be determined whether the small size of the specimens is genetic or ontogenetic

an organic geochemical investigation of crude oils from shanganning jianghan chaidamu and zhungeer basins people s republic of china abstract eighteen oils from four different oil producing basins in china have been characterized using a variety of organic geochemical techniques the source materials for these oils were deposited under a variety of environmental conditions and this study investigates the use of geochemical parameters in differentiating the resultant oils the parameters discussed are based on relative amounts and distributions of both individual and groups of biomarkers including organosulphur compounds and the carbon isotopic composition of the aliphatic and aromatic fractions examination of the oils showed that those from the zhungeer basin thought to be derived from source rocks formed in a brackish lacustrine environment possessed high concentrations of tricyclic terpanes relative to pentacyclic hopanes and a predominance of 24 methyl and 24 ethylcholestanes c28 and c29 respectively over cholestanes c27 which were virtually absent oils believed to be derived from source rocks deposited in the saline depositional environment of the jianghan basin were characterized by a large amount of gammacerane relative to 17 21 30 homohopanes c31 22r and 22s in general those oils considered to be derived from source rocks deposited in fresh water lacustrine environments shanganning and chaidamu basins had small amounts of tricyclic terpanes relative to pentacyclic hopanes the presence of an unknown c30 pentacyclic terpane small amounts of extended hopanes c31 c35 relative to 17 21 hopane and relatively large amounts of 24 ethylcholestanes 20r and 20s relative to total stearanes it appears therefore that the distribution of biomarkers may be used to differentiate oils derived from different lacustrine environments

heterogeneity of oil composition within a reservoir as a reflection of accumulation history abstract the unaltered petroleums of a small oil field in the f r germany reveal pronounced spatial heterogeneities in bulk and molecular composition over most of the field area the oil in high porosity high permeability sand intervals bears a higher proportion of saturated hydrocarbons and has a higher maturity chemical signature as compared to oils occupying lower porosity lower permeability zones for all sands with less than about 13 porosity a regular relationship was observed between oil composition and porosity permeability with a decrease of the latter petrophysical properties increasingly lower chemical maturities and increasingly different bulk chemical compositions lower proportions of saturated hydrocarbons and higher proportions of nso compounds were recorded maximum contrasts measured for chemical maturities are e g 0 63 versus 0 82 vitrinite reflectance equivalents rc values calculated on the basis of the methylphenanthrene index according to radke and welte 1983 0 31 versus 0 84 for the ratio of triaromatic to mono plus triaromatic steroid hydrocarbons and 0 38 versus 0 47 for the 20s 20s 20r ratio of c29 5 h 14 h 17 h steranes these spatial heterogeneities in the composition of the oils are interpreted to reflect 1 i successive stages of trap filling due to episodes of increasing burial and maturation of the relevant source rocks in combination with 2 ii low rates of in reservoir mixing of these individual oil charges by convection or diffusion recognition of compositional heterogeneities within the oil column of individual fields may not only provide a basis for the reconstruction of reservoir filling history but may also have important implications for improving petroleum production

geochemistry of palaeozoic marine petroleum from the tarim basin nw china part 1 oil family classification abstract a series of palaeozoic marine oils ranging from condensates to very heavy oils from the cratonic region of the tarim basin nw china have been examined to delineate oil families crude oils from the mesozoic foreland kuqa depression were also analyzed for comparison the genetic family was assessed using bulk hydrocarbon isotopic composition alkylation pattern of polycyclic aromatic hydrocarbons pahs and biomarker distributions detailed oil oil correlation suggests two distinct families occur in the cratonic region despite the diversity of the reservoir rocks and some variability in oil physical properties the tabei and tazhong oils are classified in general into a single family with a possible indication for secondary subdivision these oils are characterized by low pristane phytane pr ph ratio high dibenzothiophene phenanthrene dbt p ratio light bulk isotopic composition high degree of pah alkylation high proportion of c23 and c24 tricyclic terpanes and low abundance of c24 tetracyclic terpane and triaromatic dinosteroids this family is inferred to have a middle upper ordovician source rock the tadong family distinctly different from the tabei and tazhong families is characterized by relatively high pr ph ratio low dbt p ratio slightly heavier bulk isotopic compositions and low degree of pah alkylation it also has a unique biomarker signature with a high proportion of triaromatic dinosteroids possibly indicating cambrian lower ordovician source rocks the oils from the kuqa depression are easily distinguished from the other two families due to their terrigenous origin the major characteristics of the kuqa oils are high pr ph ratio very low dbt p ratio heavy bulk isotopic composition low pah alkylation degree high proportion of c20 and c21 tricyclic terpanes and c24 tetracylic terpane and abundance of triaromatic dinosteranes and 4 methyl 24 ethyltriaromatic cholestanes these characteristics are consistent with terrestrial organic source rocks deposited under sub oxic conditions

formation and evolution of solid bitumen during oil cracking abstract solid bitumen is widespread throughout lower paleozoic paleo reservoirs in southern china however the processes that control its formation and evolution remain unclear here we document temporal changes in the yield and characteristics of solid bitumen generated during oil cracking using an experimental approach involving the anhydrous pyrolysis of crude oil the results indicate that solid bitumen is predominantly produced in environments of high thermal maturity associated with the dry gas stage of oil cracking i e during rapid methane generation and c2 c5 gaseous hydrocarbon destruction with maximum solid bitumen yields up to about 42 of the original amount of crude oil a near linear relationship exists between solid bitumen yields and methane abundance during the main stage of solid bitumen formation although there is no clear variation in the 13c values of solid bitumen produced at any stage of this process this suggests that the isotopic composition and distribution of solid bitumen within a reservoir can be used to identify hydrocarbon sources delineate the range of paleo reservoirs and assess the size of paleo oil reservoirs and oil cracked gas reservoirs within a basin

effects of h2o on phase relations during crystallization of gabbros in the kap edvard holm complex east greenland in the kap edvard holm complex of east greenland layered monly results in the formation of discordant igneous bodies within crystallizing cumulus sequences in some olivine gabbros host numerous small discordant bodies of ultramafic cases partially molten cumulates appear to have reacted rock and magnetite gabbro that formed by late magmatic metasomatic with liquids or fluids that originated within the cumulus replacement of partially solidified gabbroic cumulates similar repile resulting in resorption of cumulus minerals crysplacive rocks are also present as large semi conformable sheet like tallization of intrusive or replacive bodies and rebodies within the layered gabbro sequence replacive bodies of all distribution of mass within the intrusion e g robins sizes are spatially associated with xenoliths of metabasaltic lava 1982 butcher 1985 butcher et al 1985 helz 1987 the small bodies cluster around xenoliths and the large bodies host irvine 1987 boudreau 1988 mcbirney sonnenthal swarms of xenoliths the replacive bodies are inferred to have formed 1990 larsen brooks 1994 scoon mitchell 1994 by reaction of gabbroic cumulates with pore liquids that were mathez 1995 meurer et al 1997 boudreau 1999 in enriched in h2o by degassing or dehydration melting of the other cases partially molten cumulates are inferred to metabasalts as these liquids migrated through the cumulus pile have reacted with externally derived magmas that inthey resorbed plagioclase and produced ultramafic bodies where the truded the cumulus pile resulting in the development liquids came to rest they reacted with gabbroic cumulates to produce of discordant replacive bodies via the reaction of the bodies of magnetite rich gabbro the most evolved pore liquids cumulates with intruding magmas e g morse et al 1987 segregated to form hornblende rich pegmatitic dikes of roughly dacitic bedard et al 1988 tegner wilson 1993 tegner composition suggesting that hydration and possibly oxidation of the robins 1996 because cumulus rocks preserve records magma shifted the liquid line of descent from a tholeiitic trend toward of magmatic fractionation and replenishment in large a calc alkaline trend these inferences imply that contamination of mafic intrusions recognizing and understanding postmagmas by dehydration of hydrothermally altered crustal rocks may cumulus processes such as these can provide insights significantly influence the evolution of mafic magma systems into the evolution of mafic magma chambers and the differentiation of basaltic magmas within the crust near the western margin of the kap edvard holm

chemical and petrographic evidence for thermal cracking and thermochemical sulfate reduction of paleo oil accumulations in the ne sichuan basin china significant extents of heterogeneity are observed in the optical properties reflectance values and s c atomic ratio values of solid bitumens in the carbonate reservoirs of the lower triassic feixianguan and changxing formations in the puguang gas field the largest in marine carbonates in china the chemical and stable carbon isotope compositions of the gaseous alkanes in the produced gases also depend on field location with no clear correlation with the hydrogen sulfate content these data indicate that the gas reservoirs are highly compartmentalized this manuscript describes an integrated chemical and petrographic approach for distinguishing solid bitumens formed by thermal cracking and by thermochemical sulfate reduction tsr the fact that most reservoir bitumens have only been partially affected by tsr suggests that sulfate supply appears to be a major limiting factor for the tsr reactions involving gaseous alkanes

an re os date for molybdenite bearing quartz vein mineralization within the kangerlussuaq alkaline complex east greenland implications for the timing of regional metallogenesis the kangerlussuaq alkaline complex east greenland is one of the largest alkaline complexes in the world it is known to host a number of occurrences of base and precious metal mineralization including the flammefjeld porphyry mo deposits and a suite of epithermal style base and precious metal veins in an area around the sondre syenitgletscher here we describe and date a previously unknown occurrence of molybdenite pyrite scheelite bearing quartz veins associated with alkali basalt dikes that intrude the main syenites of the complex the veins appear to be cogenetic with the dikes which crosscut and brecciate granodiorites of the cirque 1320 complex sulfur isotope signatures of molybdenite and pyrite in the veins give a tight range with mean 34 s of 2 2 0 7 consistent with a magmatic s source related to the intrusion of the dikes molybdenite from the veins gave an re os age of 52 74 0 26 ma some 13 m y older than molybdenite at the flammefjeld porphyry deposit thus distinguishing this metallogenic episode as a distinct event temporally unrelated to the known mo mineralization at flammefjeld significantly in terms of the timing of regional metallogenesis and magmatism our date suggests that the age of the kangerlussuaq alkaline complex itself may be slightly older than the 50 ma currently accepted based on 40 ar 39 ar dating from biotites in the main syenites given the common discrepancy in ore systems of 40 ar 39 ar which produce slightly younger dates than those by re os and u pb we suggest the actual age of the kangerlussuaq alkaline complex may be closer to 53 to 52 ma

longmen shan fold thrust belt and its relation to the western sichuan basin in central china new insights from hydrocarbon exploration the longmen shan fold thrust belt is one of the key regions of demonstrable mesozoic cenozoic tectonic evolution in china and the sichuan basin was the first natural gas producing area in china in this article the structural features of the longmen shan belt are presented using both seismic profiles and field data the complex structures of the northeast trending longmen shan fold thrust belt and its foreland in the western sichuan basin are formed by southeast directed thrusting several eastward verging rootless thrust sheets and imbricates of cambrian triassic rocks have been recognized in the northern longmen shan belt evidence suggests that the northern longmen shan belt experienced at least two major periods of deformation in the late triassic and cenozoic however the southern longmen shan belt is represented by the basement involved thrust structures and klippen and its major periods of deformation were in the latest cretaceous early cenozoic sedimentary features in the western sichuan basin reflect a two phase flexural loading history and illustrate that the late triassic foreland basin extends along the foredeep of the entire length of the longmen shan belt but the uppermost cretaceous paleogene rejuvenated foreland basin is restricted in the southern part of the western sichuan basin structural geometries suggest that prospective traps are mainly developed in the frontal zone of the longmen shan fold thrust belt and in the southern part of the western sichuan basin one of the major contributions of this article is finding preexisting paleozoic rift basins under the cenozoic thin skinned thrust belts which represent a new potential hydrocarbon play

reflectance measurements of zooclasts and solid bitumen in lower paleozoic shales southern scandinavia correlation to vitrinite reflectance abstract reflectance measurements have been carried out on zooclasts graptolites chitinozoans and vase shaped microfossils and other organic particles vitrinite like particles porous granular vitrinite like particles and solid bitumen in middle cambrian to upper silurian shales from central and southern sweden and the danish island of bornholm baltic sea the most abundant organic components in all the shales are fragments of graptolites and vitrinite like particles the reflectance distribution of these two types of components is largely identical and it is suggested that the vitrinite like particles are fragments of graptolites without any recognizable morphology reflectance measurements of graptolites and vitrinite like particles yield well defined reflectance populations in samples with average r graptolite and average r vitrinite like of 0 75 r o the reflectance distributions are bimodal because of increasing bireflectance and the average reflectance value of the well defined lower reflecting population is arbitrarily used as maturity indicator our results suggest that with increasing thermal maturity the reflectance of graptolites increases faster than the predicted vitrinite reflectance the relationship between graptolite reflectance and equivalent vitrinite reflectance can be expressed by the equation vr eqv 0 73 r graptolite vitrinite like low 0 16 the gas generation window which normally is considered to begin at a vitrinite reflectance of 1 3 r o in post lower paleozoic rocks containing vitrinite starts accordingly at 1 56 r o graptolite reflectance porous granular vitrinite like particles occur in minor amounts and they may represent graptolite fragments with a non smooth surface they generally yield slightly higher reflectance than non granular vitrinite like particles and graptolite fragments the middle cambrian to furongian upper cambrian shales may contain sparse fragments of vase shaped microfossils vsm that seem to follow the maturation trend of chitinozoans in the present sample set the reflectance of chitinozoans and vsm is comparable to that of graptolites at the same level of maturity reflectance measurements of solid bitumen are a poor maturity indicator probably because bitumen can have various origins and morphologies and it may not be indigenous to the host rock

the origin of pyrobitumens in upper devonian leduc formation gas reservoirs alberta canada an optical and eds study of oil to gas transformation pyrobitumens are common within deep basin devonian carbonate gas reservoirs of the western canada sedimentary basin incident light microscopy and sem eds have been used to study the origin of pyrobitumens from upper devonian isolated reefs of the leduc formation west central alberta reflectance properties romax and romin coke microtextures and relative s c ratios are used to classify the pyrobitumens in portions of reservoir units where nso enriched low aromaticity crudes may have been dominant oil to gas transformations produced mainly low reflecting isotropic to fine grained mosaic coke microtextures within the reservoir pyrobitumens type a in contrast where normal crudes were most likely dominant in the reservoir units prior to thermal cracking pyrobitumens with high bireflectance and very anisotropic coarse flow to domain cokes dominate type b oil to gas cracking within some of the reservoir units resulted in overpressuring and is represented by highly deformed pyrobitumens with fibrous coke textures and high bireflectance relative concentrations of type a and b pyrobitumens vary vertically and temporally in some of the reefal buildups the variations in the dominant pyrobitumen types are attributed to crude oil alteration which preceded crude oil to gas transformation e g tar mats in some zones whereas other zones may have been altered contemporaneously with crude oil cracking the later may have resulted from the oxidation and sulphur enrichment of the crude oil during thermochemical sulphate reduction this reaction is prevalent within devonian evaporite carbonate strata of the western canada sedimentary basin generating copious volumes of h2s the interaction between crude oil and sulphur enriched highly alkaline fluids is suggested by the presence of high s c very fine grained late stage calcined needle cokes within brecciated pyrobitumens

assimilation and fractionation in adjacent parts of the same magme chamber vandfaldsdalen macrodike east greenland the vandfaldsdalen macrodike which lies in the skaergaard region of east greenland is a remarkably zoned fossil magma chamber with a granophyric cap overlying cumulate gabboros the intrusion is distinctly bimodal with a large compositional discontinuity at the contact between the gabbro and granophyre although the exposed part of the macrodike is in contact with tertiary basalts and sediments the granophyre originated by assimilation of xenoliths derived from the underlying archean basement sr and nd isotopic ratios throughout the cumulate sequence are remarkably similar indicating insignificant contamination of the gabbro by the granophyre modelling of the compositional effects of cooling and crystallization indicate that the cumulate pile resulted from fractional crystallization with the complicating effects of trapped liquid and post cumulus fractionation the uppermost rocks in the mafic part of the chamber sio2 62 feo 12 4 resulted from about 85 fractional crystallization a transgressive sill of strongly fractionated magma sio2 67 feo 8 8 formed from extracted intercumulus liquid that was the result of 90 fractional crystallization of the original magma mass balance indicates that typical granophyre is made up of about 75 dissolved xenoliths by weight and 25 mantle derived basaltic magma the magmas were not measurably affected by material exchange across the interface between the gabbro and granophyre this magma chamber evolved by both assimilation and fractional crystallization but the residual liquids formed by fractional crystallization were unaffected by assimilation heat exchange between were unaffected by assimilation heat exchange between the two parts of the chamber was obviously important but there was insignificant material exchange the inability of fractional crystallization and assimilation to affect the same liquid is related to the dynamic behavior of this particular magma chamber particularly the buoyancy of granophyre relative to evolving tholeiitic magma

the end cretaceous dinosaur succession in europe the tremp basin record spain abstract the succession of maastrichtian deposits in the tremp basin south pyrenean area spain has provided long sections with numerous dinosaur sites found in the aren and tremp formations the dinosaur record consists on titanosaur sauropods dromaeosaurid theropods hadrosaur ornithopods including lambeosaurines and nodosaurid ankylosaurians correlation of the sections enabled a clear succession of dinosaur localities to be established and thereby the succession of dinosaur faunas titanosaur remains are present throughout the series but are particularly abundant in the basal strata theropods and hadrosaur ornithopods are found all through the series lambeosaurine hadrosaur remains are restricted to sandstone channel beds close to the k t boundary the palaeoenvironmental conditions in each site were deduced from the sedimentological study which allows establishing a relationship between environments and dinosaur taxa and thus the over or under representation of taxa in the vertical succession to be unravelled titanosaurs and ornithopods are common in but not exclusive to marine to continental transitional and continental environments respectively ankylosaurians are so far restricted to marine to continental transitional environments but the sample is scarce the fossil richness and the possibility of correlations among the different local sections make the tremp basin one of the best places in europe to understand the final history on non avian dinosaurs the fossil record from the tremp basin suggests that they were well diversified during the whole maastrichtian until their extinction as observed in north america and asia sauropods were still present at the end of the maastrichtian and lambeosaurines occurred at least in the upper part of the maastrichtian

origin of the transgressive granophyres from the layered series of the skaergaard intrusion east greenland abstract the transgressive granophyres are a swarm of silicic dikes and sills in the layered series of the skaergaard intrusion that range in composition from ferrodiorites to granites although originally thought to be derived by differentiation of skaergaard magma accumulated evidence indicates that the origin of these granophyres is more complex and involves contributions from melted country rocks in the present study it is shown that field relations are inconsistent with any genetic relationship between the transgressive granophyres from the layered series and differentiated skaergaard magma although new sr isotope analyses confirm that these granophyres are at least partly derived by fusion of archean country rock field relations preclude derivation of this crustal component from partially melted gneissic xenoliths from the skaergaard magma chamber or from melting along the contact between the gneisses and the skaergaard pluton major and trace element compositions together with sr isotope ratios indicate that the transgressive granophyres from the layered series represent a cogenetic suite of magmas related to each other primarily by a closed system process such as crystal fractionation and that the parental magma that gave rise to these granophyres was formed beneath the skaergaard intrusion by contamination of differentiated post skaergaard mafic magmas with partially fused archean crust

application of organic petrography in north american shale petroleum systems a review abstract organic petrography via incident light microscopy has broad application to shale petroleum systems including delineation of thermal maturity windows and determination of organo facies incident light microscopy allows practitioners the ability to identify various types of organic components and demonstrates that solid bitumen is the dominant organic matter occurring in shale plays of peak oil and gas window thermal maturity whereas oil prone type i ii kerogens have converted to hydrocarbons and are not present high magnification sem observation of an interconnected organic porosity occurring in the solid bitumen of thermally mature shale reservoirs has enabled major advances in our understanding of hydrocarbon migration and storage in shale but suffers from inability to confirm the type of organic matter present herein we review organic petrography applications in the north american shale plays through discussion of incident light photographic examples in the first part of the manuscript we provide basic practical information on the measurement of organic reflectance and outline fluorescence microscopy and other petrographic approaches to the determination of thermal maturity in the second half of the paper we discuss applications of organic petrography and sem in all of the major shale petroleum systems in north america including tight oil plays such as the bakken eagle ford and niobrara and shale gas and condensate plays including the barnett duvernay haynesville bossier marcellus utica and woodford among others our review suggests systematic research employing correlative high resolution imaging techniques and in situ geochemical probing is needed to better document hydrocarbon storage migration and wettability properties of solid bitumen at the pressure and temperature conditions of shale reservoirs

chronostratigraphic synthesis of the latest cretaceous dinosaur turnover in south western europe abstract in south western europe the uppermost cretaceous continental deposits in the different sedimentary basins of iberia portugal and north and central spain the pyrenees spain and france as well as languedoc and provence southern france provide one of the few terrestrial records that allow a comprehensive study of the campanian maastrichtian dinosaur assemblages for the last years the southern pyrenees has been the target of intense geological palaeontological and geochronological research hundreds of fossil localities are now framed in high resolution lithological sections the succession of these sites most of them located in the tremp syncline is based on the physical correlation of rock bodies as permitted by the general outcropping conditions outside this syncline correlation is supported by geochronologic and biostratigraphic data mainly magnetostratigraphy and planktic foraminifera biostratigraphy the integration of the entire dataset sheds new light on the maastrichtian dinosaur turnover characterized by a shift from a sauropod dominated to a hadrosauroid dominated faunal assemblage this turnover was progressive and involved immigrants from north america eurasia and gondwana which probably reached the study area after a sea level drop this faunal change was mainly triggered by the arrival of lambeosaurine hadrosauroids a group that rapidly displaced the rest of the herbivorous clades of the region some of the extinction events suffered by the pre turnover faunas during the maastrichtian coincide with marine isotopic and sea level drop events suggesting that faunal competition was not the only cause of the observed changes in dinosaur composition despite this faunal replacement the resulting ecosystem after the turnover shows no major loss of biodiversity before the cretaceous paleogene extinction event

the influence of solid reservoir bitumen on reservoir quality 1 reservoir bitumen precipitates in pore systems from the alteration of trapped or migrating oil in carbonate and siliciclastic reservoirs reservoir bitumen is not readily identified on typical log suites where it is read as open porosity which has hampered its broad recognition as a reservoir altering cement when present as a solid it can be as influential on reservoir quality as carbonate silica or authigenic clay cements and should therefore be evaluated as part of the diagenetic evolution of any pore system whenever encountered five morphotypes of reservoir bitumen have been identified and named droplets carpets peanut brittle vesicular and digitate data from east texas gulf coast and west african examples indicate that reservoir bitumen can significantly reduce total effective porosity permeability can be significantly reduced by restricted or closed pore throats and by fines migration even when bitumen occurs in only moderate amounts the occurrence and distribution of bitumen on well field and regional scales can range from uniform and predictable to irregular and unpredictable but mappable through examination of core and cuttings within a trap bitumen can cause heterogeneity and form permeability barriers not related to depositional facies or pre bitumen diagenesis and reservoir quality it economic importance must be recognized when reservoir parameters are adversely affected impacting reserves calculations recovery factors and secondary recovery programs on a regional scale predictive models can be developed to determine the areas of a trend or portions of a stratigraphic section that are most likely to be affected and these models can be incorporated with other data for evaluating expected reservoir quality in regional play assessments

three common source rock evaluation errors made by geologists during prospect or play appraisals geologists are frequently called on to evaluate the source rocks associated with their exploration prospects or plays the three most common questions asked and answered about the source rock during project reviews are what s the total organic carbon toc what kerogen type does rock eval indicate and what maturity level does the vitrinite reflectance data point to the answers to these seemingly innocuous questions may in fact be providing a false sense of security about the source rock in question understanding how this line of questioning can lead you astray and make you the victim of the toc myth if i have high toc i have a good source rock the rock eval fallacy the rock eval data tell me what kind of kerogen is in my source rock and the vitrinite reflectance deficiency vitrinite reflectance will tell me if my source rock is generating is important some of the solutions to these problems include fully integrating toc and rock eval data supplementing rock eval data with pyrolysis gas chromatography and using burial history diagrams to help interpret vitrinite reflectance harry dembicki jr is a senior geological advisor for geochemistry in the geological technology group at anadarko petroleum corporation where he provides technical support to both exploration and development teams he holds a b s degree 1973 in geology from the state university college of new york at new paltz and a ph d 1977 in geology with emphasis in organic geochemistry from indiana university he previously worked as an organic geochemist for conoco and marathon

effects of oil cracking on fluorescence color homogenization temperature and trapping pressure reconstruction of oil inclusions from deeply buried reservoirs in the northern dongying depression bohai bay basin china the effects of oil cracking on fluorescence color homogenization temperature tho and trapping pressure pt of oil inclusions from deeply buried reservoirs dbrs 3672 4359 m in the northern dongying depression were determined based on fluorescence spectroscopy and homogenization temperatures of oil inclusions kinetic modeling of crude oil cracking and petroleum inclusion thermodynamics modeling the modeling results demonstrate that fluorescence color tho and predicted pt have strong relationships with the transformation rate via cracking of oil to gas tr and the formation temperature tf that the inclusions experienced the fluorescence color is hardly influenced at all during the initial stages of oil cracking tr 13 tf 160 c but fluorescence color begins to shift toward shorter wavelengths blue shift during progressive oil cracking tr 24 tf 190 c with further oil cracking the fluorescence color may either experience no change or continue its blue shift eventually the fluorescence color will disappear as the aromatic compounds are completely cracked the tho increases at first tr 24 tf 190 c but then decreases or even becomes negative during major oil cracking the reconstructed pt values show a corresponding reverse trend oil inclusions from dbrs and other shallow reservoirs in the dongying depression show an obvious blue shift in fluorescence color at a depth of approximate 4000 m tf 160 c and generally contain solid bitumen below 4000 m supporting the effect of oil cracking on fluorescence variation consistent with the modeling result the tho from dbrs in the minfeng area increases with increasing burial depth tf 190 c which is also consistent with the modeling results however the tho of oil inclusions with blue white fluorescence from dbrs in the shengtuo area did not show such a trend recent trapping high trapping pressure and higher maturity oil may have led to a low degree of oil cracking and thus less modification of tho in the shengtuo area oil cracking results in consistent volume ratios of pyrobitumen to oil inclusions fvpy in the same fluid inclusion assemblage and the fvpy value increases with oil cracking level which can be used to recognize if oil cracking has occurred in oil inclusions and what level of oil cracking they have experienced as the oil cracking model used in this study did not account for the role of pressure it is more applicable for oil inclusions that were trapped under normally pressured conditions oil inclusions trapped under overpressured conditions will be less influenced by oil cracking

solid bitumen in calcite veins from the natih formation in the oman mountains multiple phases of petroleum migration in a changing stress field abstract solid bitumen in calcite veins in natih limestone on the southern flank of the jebel akhdar anticline provide evidence for at least two previously unrecognized petroleum migration events in the oman mountains we present field observation of bituminous calcite veins combined with microscopy using highly polished thin sections this allows imaging of solid bitumen in reflected light and study of its microstructural context in transmitted light straight and en echelon black impregnated bedding normal natih a calcite veins strike 110 they formed as one of the earliest structures in an extensional stress regime at the end of cretaceous turonian santonian either by flexure of the arabian plate wasia aruma break or by subsidence during subduction the veins always contain planar arrays of small during the first migration event microfracturing during obduction of the semail ophiolite and emplacement of the hawasina thrust sheets in santonian campanian times formed pathways for oil into the veins mosaic type solid bitumen formed during further vein growth it has a higher solid bitumen reflectance br r 3 40 3 76 combined with a high optical anisotropy compared to the underlaying thermally overmature natih b source rock br r 3 10 3 14 the higher reflectance of mosaic type solid bitumen is interpreted to result from deformation and does not reflect maximum burial temperatures which are inferred to have been about 225 c the second migration event is indicated by low reflective homogeneous type solid bitumen with palaeotemperatures br r 0 86 0 92 about 145 c lower than maximum burial it occurs along pressure solution seams which cross cut the veins showing that this is the latest event in the paragenetic sequence interpreted to have formed after lateral intraformational oil migration from the active natih oil kitchen located approximately 40 km sw of the study area during doming and uplift of the oman mountains in oligocene to pliocene times

the significance of 24 norcholestanes triaromatic steroids and dinosteroids in oils and cambrian ordovician source rocks from the cratonic region of the tarim basin nw china abstract two oil families in ordovician reservoirs from the cratonic region of the tarim basin are distinguished by the distribution of regular steranes triaromatic steroids norcholestanes and dinosteroids oils with relatively lower contents of c 28 regular steranes c 26 20s c 26 20r c 27 20s and c 27 20r regular triaromatic steroids dinosteranes 24 norcholestanes and triaromatic dinosteroids originated from middle upper ordovician source rocks in contrast oils with abnormally high abundances of the above compounds are derived from cambrian and lower ordovician source rocks only a few oils have previously been reported to be of cambrian and lower ordovician origin especially in the east region of the tarim basin this study further reports the discovery of oil accumulations of cambrian and lower ordovician origin in the tabei and tazhong uplifts which indicates a potential for further discoveries involving cambrian and lower ordovician sourced oils in the tarim basin dinosteroids in petroleum and ancient sediments are generally thought to be biomarkers for dinoflagellates and 24 norcholestanes for dinoflagellates and diatoms therefore the abnormally high abundance of these compounds in extracts from the organic rich sediments in the cambrian and lower ordovician and related oils in the cratonic region of the tarim basin suggests that phytoplankton algae related to dinoflagellates have appeared and might have flourished in the tarim basin during the cambrian period steroids with less common structural configurations are underutilized and can expand understanding of the early development history of organisms as well as define petroleum systems

a pedotype approach to latest cretaceous and earliest tertiary paleosols in eastern montana a pedotype approach to the study of paleosols emphasizes individual profiles it is an alternative approach to the study of geosols which are laterally extensive suites of paleosols or pedofacies which are pedogenically distinctive sedimentary facies this is the first pedotype study of paleosols across the cretaceous tertiary boundary in eastern montana pedotypes allow assessment of sedimentation and fossilization the sequence of paleosols across the cretaceous tertiary boundary at bug creek is one of high temporal resolution because most available geological time can be accounted for by differing degree of development inferred for each pedotype paleosols at bug creek include pedotypes that preserve plant fossils well but were unfavorable for preservation of fossil vertebrates pedotypes also allow reassessment of ecosystem change despite indications of catastrophe at the cretaceous tertiary boundary the array of paleocene and cretaceous pedotypes are not strikingly different the upper cretaceous hell creek formation includes pedotypes interpreted as gleyed alfisols inceptisols and entisols probably formed under seasonally water logged forest and mean annual rainfall of the order of 900 1200 mm most paleosols of the lower paleocene tullock formation were histosols but some can be interpreted as gleyed inceptisols and entisols probably formed under bald cypress swamps in a humid climate with 1200 mm mean annual rainfall broadly comparable pedotypes were present before and after the cretaceous tertiary boundary although paleocene flood plain forest lived in paleosols chemically a little more oligotrophic than cretaceous paleosols this modest difference supports the idea that change to coaly facies in the earliest paleocene was a local shift in sedimentary environment such local changes do not begin to account for profound disruption in specific composition of plant and animal communities at the cretaceous tertiary boundary in eastern montana

the behaviour of platinum group elements in basalts from the east greenland rifted margin the continental flood basalts of the east greenland volcanic rifted margin were extruded during continental breakup above the ancestral iceland mantle plume at 55 ma three distinct magma types the low ti high ti and very high ti series lts hts and vhts respectively are found intercalated in the 6 km thick plateau lava sequence incompatible trace elements indicate that the lts are derived from a more depleted mantle source compared to hts and vhts the lts is characterised by increasing cu 105 to 248 ppm and pd 7 to 24 ppb constant cu pd ratio 10 000 and decreasing ir 1 1 to 0 05 ppb and ru 1 8 to 0 3 ppb concentrations during magmatic differentiation 16 to 7 wt mgo the constant cu pd ratio reflects silicate and chromite dominated fractionation without concurrent segregation of sulphide s undersaturated differentiation is also indicated in the hts which also displays increasing pd 6 16 ppb and decreasing ir concentrations 1 to 0 05 ppb during differentiation and the cu pd ratios for the entire series average 21 000 however some hts samples have elevated cu pd ratios up to 33 000 cu pd ratios in the hts do not correlate with mgo and this is interpreted to reflect varying cu pd ratios of hts parental magmas rather than s saturated differentiation during s undersaturated differentiation of the lts and hts pt pd ratios decrease from 1 3 to 0 11 and 1 1 to 0 2 respectively which indicates that pd is much more incompatible than pt during s undersaturated differentiation the vhts consists exclusively of highly evolved samples with low mgo 6 6 6 1 wt and pd ir ratios 98 228 here cu pd ratios increase from 17 500 to 35 000 with decreasing cr concentrations which indicate that these magmas experienced silicate fractionation with concurrent segregation of sulphide the lts represent melting of a depleted source and show high pge concentrations and constant cu pd ratios during s undersaturated differentiation melting of a normal depleted upper mantle source generates s saturated melts morb and the depleted lts source is therefore considered an extraordinary s poor component within the ancestral iceland plume of the three series the vhts contain the largest contribution from enriched mantle portions the vhts have similar pge but much higher nb concentrations for instance compared to the most evolved lts and hts samples indicating that the enriched source contributes nb but not pge

the cretaceous tertiary biotic transition mass extinctions are recognized through the study of fossil groups across event horizons and from analyses of long term trends in taxonomic richness and diversity both approaches have inherent flaws and data that once seemed reliable can be readily superseded by the discovery of new fossils and or the application of new analytical techniques herein the current state of the cretaceous tertiary k t biostratigraphical record is reviewed for most major fossil clades including calcareous nannoplankton dinoflagellates diatoms radiolaria foraminifera ostracodes scleractinian corals bryozoans brachio pods molluscs echinoderms fish amphibians reptiles and terrestrial plants macrofossils and palynomorphs these reviews take account of possible biasing factors in the fossil record in order to extract the most comprehensive picture of the k t biotic crisis available results suggest that many faunal and floral groups ostracodes bryozoa ammonite cephalopods bivalves archosaurs were in decline throughout the latest maastrichtian while others diatoms radiolaria benthic foraminifera brachiopods gastropods fish amphibians lepidosaurs terrestrial plants passed through the k t event horizon with only minor taxonomic richness and or diversity changes a few microfossil groups calcareous nannoplankton dinoflagellates planktonic foraminifera did experience a turnover of varying magnitudes in the latest maastrichtian earliest danian however many of these turnovers along with changes in ecological dominance patterns among benthic foraminifera began in the latest maastrichtian improved taxonomic estimates of the overall pattern and magnitude of the k t extinction event must await the development of more reliable systematic and phylogenetic data for all upper cretaceous clades

characterization of methane adsorption on overmature lower silurian upper ordovician shales in sichuan basin southwest china experimental results and geological implications abstract a series of methane adsorption isotherms were measured at 35 4 c 50 6 c and 65 4 c at pressures up to 15 0 mpa for eight dried overmature lower silurian upper ordovician shale samples collected from the sichuan basin with toc values in the range of 1 87 5 74 the measured maxima of excess adsorption capacity of methane range from 1 25 to 2 50 cm 3 g rock at 65 4 c the maxima are slightly enhanced at 35 4 c but all are positively correlated with total organic carbon toc both the supercritical dubinin radushkevich sdr and langmuir based excess adsorption models were found to represent the experimental excess adsorption isotherms equally well within the experimental range the temperature dependent densities of adsorbed methane resulting from the parameter fit of the sdr based excess adsorption model are in the range of 297 415 mg cm 3 for the langmuir based excess adsorption model the adjusted densities range from 386 mg cm 3 to 1027 mg cm 3 and most of them are much larger than the liquid density of methane at its boiling point 424 mg cm 3 nevertheless the maxima of absolute methane adsorption capacity fitted by both models are not significantly different and are linearly correlated one of the contributors to the uncertainty of the gas in place estimation in geological conditions is the inconsistent utilization of experimental excess sorption data as absolute sorption values particularly at high pressures however the choice of adsorption model itself langmuir or sdr based and the fitting procedure assuming either constant or temperature dependent adsorbed phase density and maximum sorption capacity do not significantly affect the estimated gips for the geological system studied here with depths of less than 4000 m

dinosaur abundance was not declining in a 3 m gap at the top of the hell creek formation montana and north dakota an 3 m stratigraphic interval that entirely lacks dinosaur fossils or has very few fossils has been reported at the top of the hell creek formation in the upper great plains of north america the presence of the 3 m gap in fossil distribution has been cited as evidence that dinosaurs had either become extinct or were on the verge of extinction prior to the bolide impact at the end of the cretaceous period a survey in two areas of north dakota and montana reveals that dinosaur fossils in the upper 3 m of the hell creek formation occur in numbers that are comparable to their abundance in other levels of the formation evidence for a gradual extinction is absent and data are consistent with an abrupt extinction associated with an impact

impact of sedimentology diagenesis and solid bitumen on the development of a tight gas grainstone reservoir in the feixianguan formation jiannan area china implications for gas exploration in tight carbonate reservoirs abstract tight gas grainstone reservoirs in the third member of the feixianguan formation jiannan area evolved from a paleo oil accumulation as evidenced from abundant solid reservoir bitumen porosity evolution of the grainstones was studied by evaluating relative influences of sedimentology diagenesis and solid bitumen formed during cracking of accumulated oils grainstones exhibited regional distinct effectiveness for paleo oil and present gas accumulations during oil window and subsequent gas window diagenesis in the southern zone where grainstones were not subjected to subaerial exposure and meteoric diagenesis in the early diagenetic stage paleoporosity at the time of oil charge was mainly controlled by sedimentologic factors e g grain size sorting and grain type and paleo oil reservoirs only occurred in the ooid dominated grainstones with good sorting and coarse grain size in contrast in the northern zone meteoric diagenesis was responsible for paleoporosity preservation due to the early mineral stabilization of grains and meteoric calcite cementation which caused grainstones greater resistance to compaction hence most of the grainstones in the northern zone regardless of textural variables formed effective reservoirs for paleo oil accumulation as the oil cracked to gas with increasing depth and temperature during the late oil window and initial gas window solid bitumen occluded reservoir pores to varying degrees and caused paleo oil reservoirs to be significantly heterogeneous or completely ineffective for gas accumulation in contrast most grainstones that were once ineffective oil reservoirs transformed into effective gas reservoirs due to no or minor influence of solid bitumen precipitation the model of reservoir transformation development of tight grainstones provides a plausible explanation for key observations concerning the diagenetic and distribution differences between paleo oil and present gas reservoirs it is useful in predicting the distribution of potential reservoirs in carbonate strata in future exploration

solid bitumens an assessment of their characteristics genesis and role in geological processes familiar since antiquity and subject in contemporary times to various characterization schemes the exact nature of solid bitumen is not yet fully known bitumens have random polymer like molecular structures are mobile as highly viscous fluids or were once fluids but have since turned into solids solid bitumens consist mainly of large moieties of polyclyclic aromatic hydrocarbons occasionally with finely admixed fine grained cryptocrystalline graphite solid bitumens are distinguished from kerogen which is the syngenetic and generally finely dispersed particulate organic matter in sedimentary rock that virtually does not migrate following its deposition occurrences of solid bitumens are relevant to petroleum exploration as well as the search for and evaluation of a variety of metallic mineral deposits genesis of bitumen is in many cases linked to the thermal and hydrothermal history of organic matter in sedimentary rock apparently bitumen or more specifically organic acids generated along with bitumen during diagenesis may alter porosity of reservoir rocks or otherwise prepare the ground for ore deposition bitumen is also relatively sensitive to alteration processes some of which such as oxidative weathering water leaching biodegradation contact metamorphism and ionizing radiation may likewise affect its nature elemental composition of bitumen commonly reflects the nature of mineral deposits is is possible that in petroleum exploration trace metal abundances of bitumen may eventually allow prediction of crude oil types and volumes anticipated from a given source rock beside transition elements notably ni and v highly anomalous concentrations of u pt and au occur in some solid bitumens during the generation of petroleum from kerogen the trend in 13c is toward lighter values the opposite seems to occur when liquid petroleum is subjected to thermal cracking and or related processes yielding solid bitumen enriched in 13c and isotopically light methane in fact except for deasphalting and possibly some irradiation processes the result of thermal cracking oxidation water leaching inspissation drying and bacterial degradation of crude oil is that lower molecular weight hydrocarbons are removed leaving bitumen residues enriched in aromatic hydrocarbons heteroatomic compounds nso and 13c such phenomena are relevant to bitumen paragenesis in petroleum reservoir rocks to certain phanerozoic occurrences of multiple generations of bitumens and to bitumens in mineral deposits

geological setting of vertebrate microfossil localities across the cretaceous paleogene boundary in southwestern saskatchewan canada the frenchman and ravenscrag formations of southwestern saskatchewan canada record an apparently continuous sequence of nonmarine clastic sediments across the cretaceous paleogene k pg boundary extensive exposures of these fossil rich sediments occur in the frenchman river valley near the towns of ravenscrag eastend and shaunavon and have been a focus of study since the 1970s despite this long history of investigation a comprehensive account of the geographic and stratigraphic positions of many of the significant fossil localities has yet to be published given this state of affairs the goals of this paper are to i document the geographic locations stratigraphic positions and lithologies of 11 key vertebrate microfossil localities including several new localities that have been recently discovered and ii provide an update on the status of these fossil localities the majority of which have not been sampled in the last 20 years four fossil localities are known from the lower paleocene

effect of thermal maturation on chemical structure and nanomechanical properties of solid bitumen abstract an abundance of organic matter is present as solid bitumen in highly mature shales changes in chemical structure of solid bitumen during catagenesis could alter the way its mechanical properties evolve this study considers a series of solid bitumen samples artificially produced from the pyrolysis at 420 618 c of soluble organic matter which originated from maoming shale to examine alternations in their chemical structure nano morphological and mechanical properties during maturation solid state 13c nuclear magnetic resonance spectroscopy and elemental analysis were employed to characterize the structural changes young s modulus and microstructures were determined by atomic force microscopy the results show that both structural including c h atomic ratio and carbon aromaticity and mechanical young s modulus variations in solid bitumen exhibit two staged evolutions i e wet gas stage and dry gas stage during maturation in the wet gas stage easyro 1 85 2 64 the c h ratio and carbon aromaticity increase substantially with maturation and the solid bitumen is relatively compliant with an average young s modulus varying from 2 7 0 6 to 3 0 0 6 gpa when maturity reaches to dry gas stage easyro 2 64 4 59 structural parameters do not change greatly whereas solid bitumen becomes much stiffer with modulus rising sharply to 7 2 1 1 gpa at easyro 3 49 and further gently to 8 8 1 4 gpa at easyro 4 59 concomitantly great variations are observed on surface morphology and the degree of heterogeneity in solid bitumen is recorded to be increasingly high along thermal simulation given the strong correlation between structural parameters and young s modulus we suggest that the stiffening of solid bitumen is extensively affected by its structural condensation due to the loss of aliphatic carbons and the increase of aromaticity

the chronostratigraphic framework of the south pyrenean maastrichtian succession reappraised implications for basin development and end cretaceous dinosaur faunal turnover abstract the evolution of the end cretaceous terrestrial ecosystems and faunas outside of north america is largely restricted to the european archipelago the information scattered in this last area can only be integrated in a chronostratigraphic framework on the basis of robust age constraints and stratigraphy therefore we have revisited the puzzling age calibration of the sedimentary infilling from the isona sector in the tremp syncline south central pyrenees an area renowned for its rich maastrichtian dinosaur fossil record aiming to shed light to existing controversial age determinations we carried out a new magnetostratigraphic study along the 420 m long orcau and nerets sections of that area our results reveal that most of the succession correlates to the early maastrichtian mostly chron c31r in accordance to ages proposed by recent planktonic foraminifera biostratigraphy the resulting chronostratigraphic framework of the entire maastrichtian basin recorded in the tremp syncline shows that a significant sedimentary hiatus of about 3 my characterizes most of the late maastrichtian in the study area this hiatus related to an abrupt migration of the basin depocenter is temporally close to similar hiatuses decreases in sedimentary rates and facies shifts recorded in other southwestern european areas the present chronologic framework sets the basis for a thorough assessment of end cretaceous terrestrial faunal turnover and extinction patterns and the establishment of a more rigorous pyrenean basin evolution analysis

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

understanding and distinguishing reflectance measurements of solid bitumen and vitrinite using hydrous pyrolysis implications to petroleum assessment solid bitumen is a common organic component of thermally mature shales and typically is identified by embayment against euhedral mineral terminations and by groundmass textures however because these textures are not always present solid bitumen can be easily misidentified as vitrinite hydrous pyrolysis experiments 72 hours 300 360 c on shale and coal samples show solid bitumen reflectance bro in shales is less responsive to thermal stress than vitrinite reflectance vro in coal this effect is most pronounced at lower experimental temperatures 300 320 c whereas reflectance changes are more similar at higher temperatures 340 360 c neither a vitrinite like maceral or suppressed vitrinite was identified or measured in our sample set rather the experiments show that solid bitumen matures slower than vitrinite the data may explain some reports of vitrinite reflectance suppression particularly at lower thermal maturity vro 1 0 as a simple case of solid bitumen being mistaken for vitrinite further the experimental results confirm previous empirical observations that vro and bro are more similar at higher maturities vro 1 0 it is suggested that vitrinite reflectance suppression commonly reported from upper paleozoic marine shales of early to mid oil window maturity is a misnomer this observation has important implications to petroleum exploration models and resource assessment because it may change interpretations for the timing and spatial locations of kerogen maturation and petroleum generation