biological markers in lower jurassic synrift lacustrine black shales hartford basin connecticut u s a abstract the east berlin formation lower jurassic hartford basin connecticut u s a is distinctive for its six cyclic units of lacustrine black shale and gray mudstone separated by playa and fluvial redbeds the black shales are each about a meter thick and were deposited in subtropical thermally strastified oligomictic lakes the youngest of which lakes 3 through 6 were large enough to flood most of the basin and attained depths of several tens of meters the saturate fractions of solvent extracts of organic rich black shales from each of the six lakes collected at fresh roadcuts near east berlin are dominated by extended homologous series of n alkanes alkylcyclohexanes and branched chain alkanes a striking feature of the black shales is the presence of a series of extended tricyclic terpanes from c20 to at least c41 hopanes are either not detectable or present only in subordinate quantities relative to the tricyclic terpanes the samples are depleted in hopanes in part because of the elevated maturity level mid to late oil window tricyclic terpane concentrations may also have been enhanced by fractionation effects related to oil expulsion out of the black shales in addition the original organic matter may have been exceptionally rich in tricyclic terpane precursors i e fossil lipids of prokaryotes present in anoxic moderately saline alkaline lakes

remagnetization of the coast range ophiolite and lower part of the great valley sequence in northern california and southwest oregon overprinted magnetizations have been found at four localities in the middle jurassic coast range ophiolite and the overlying upper jurassic and lower cretaceous great valley sequence in northern california and at one locality in the partially correlative lower cretaceous days creek formation in southwest oregon at del puerto canyon on the east side of the diablo range a pilot study of the upper jurassic lotta creek formation gives in situ paleomagnetic directions grouped around the present geomagnetic field suggesting magnetic overprinting long after deposition and folding we suggest that the loss of original magnetization could be the result of long burial at about 7 km depth followed by late tertiary uplift the possibility of chemical remagnetization however can not be excluded paleomagnetic data from sandstones from the lower cretaceous great valley sequence in the wilbur springs area suggest cenozoic remagnetization that could be related to pliocene and pleistocene volcanic and hydrothermal activity in the area the results from calcareous concretions in the wilbur springs area from 21 sites from basalts and overlying sedimentary rocks of the great valley sequence at stonyford and from several sites in various rock types in the coast range ophiolite and great valley sequence near paskenta suggest unblocking of magnetization during the long period of burial at depth of 7 km or more and remagnetization during tectonic uplift in the late cretaceous or tertiary chemical remagnetization however can not be excluded the paleomagnetic data from six sites in lower cretaceous sedimentary rocks of the days creek formation in southwest oregon which overlies a dismembered ophiolite fail the fold test in situ paleomagnetic directions group near the expected tertiary field directions these sedimentary rocks may have been remagnetized during a major eocene tectonic event known to have occurred in this region the paleomagnetic results confirm that the coast range ophiolite and the seemingly little deformed great valley sequence in northern california as well as correlative rocks in southwest oregon have had a complex tectonic history once the nature and timing of these events are better understood the timing of remagnetization may be further constrained which in turn could give further insight into the nature of the tectonic events

organic geochemistry of a lower jurassic synrift lacustrine sequence hartford basin connecticut u s a abstract synrift terrestrial strata of the lower jurassic east berlin formation hanford basin connecticut u s a record cyclical expansion and contraction of major lakes six of which were deep enough to develop anoxic bottom waters we have studied one representative lacustrine sequence in detail sampling a new roadcut near the village of east berlin the section examined is 4 m thick with a gray silstone at the base deposited in shallow water overlain by an organic rich black shale deep water succeeded in turn by another gray siltstone deposited as the lake waters gradually receded the upper gray siltstone is chemically distinct from the lower siltstone as it contains small amounts of corrensite analcime and gypsum reflecting the increasing salinity and alkalinity of the contracting lake the samples in the center of the black shale unit contain laminae of thermally altered yellowish orange fluorescing mottled telalginite the fluorescence properties indicate a peak oil generation maturity level confirmed by a vitrinite reflectance of 1 13 and a methylphenanthrene index of 1 08 the other samples have less organic matter becoming increasingly lean towards the top and bottom of the sequence samples in the middle of the black shale unit are distinguished by the presence of an homologous series of tricyclic terpanes extending from c20 to at least c41 and by the near absence of hopanes and steranes moving upsection into the gray siltstone the samples contain markedly lessextractable organic material eom and the concentration of tricyclic terpanes relative to hopanes steadily decreases in the uppermost sample hopanes are the predominant terpanes moving downsection from the black shale into the lower gray siltstone eom and the ratio of tricyclic terpanes also decrease except in the lowermost samples which contain terpane distributions like those of the middle part of the black shale this likely is migrated material because bitumen fills microfractures and extensive megafractures the lack of hopanes and steranes in the black shales cannot simply be a maturation effect as these biomarkers appear in the adjacent beds instead the manual terpane distributions may indicate a changing depositional environment documenting the geochemical evolution of the lake or more likely they may result from fractionation during expulsion of petroleum from these mature source rocks

a suggestion for the origin of mesoscopic fabric in accretionary melange based on features observed in the chrystalls beach complex south island new zealand the chrystalls beach complex a probable accretionary melange of triassic age cropping out in south island new zealand contains a distinctive set of mesoscopic structures all of which contribute to the typically chaotic appearance of the melange these structures are 1 soft sediment bedding pull aparts 2 weakly developed slaty cleavage 3 folds in dismembered bedding with slaty cleavage as the axial surface foliation and 4 quartz fiber lineated shear surfaces analysis of overprinting relations indicates that these structures formed during a single progressive deformation rather than in several discrete events as such they record a change in response to incremental strain from initial ductile behavior toward one dominated by brittle failure it is suggested that this variation resulted from progressive dewatering during shallow level accretion at the base of an inner trench slope

dibenzothiophenes in solid bitumens use of molecular markers to trace paleo oil filling orientations in the lower cambrian reservoir of the moxi gaoshiti bulge sichuan basin southern china abstract the moxi gaoshiti mg bulge of the sichuan basin in southwestern china is unique because of its enormous gas field in old cambrian and proterozoic marine strata where oils in carbonate reservoirs have been nearly completely cracked to solid bitumen and natural gas because of high to post mature thermal maturity levels numerous solid bitumen bearing dolomites obtained from boreholes in the mg bulge provide an ideal opportunity to trace the major filling orientations for the lower cambrian paleo oil reservoirs biomarker analysis was conducted on solid bitumens through quantitative detection with gas chromatography mass spectrometry results show that all solid bitumen samples in the mg bulge exhibit similar compositions of molecular markers thereby implying that they belong to the same oil population and that paleo oils should be derived from the same source kitchen bed low pristane phytane and dibenzothiophene dbt phenanthrene ratios as well as the predominance of dbt among dbt dibenzofuran and fluorene are observed in the solid bitumen samples which suggest that related paleo oil reservoirs likely originated from a highly reducing marine shale environment all isopleth maps of the dbt concentrations 4 methyldbt 1 methyldbt 4 6 dimethyldbt 1 4 1 6 dimethyldbt dmdbt and 2 6 3 6 dmdbt 1 4 1 6 dmdbt ratios consistently indicate that the overall orientation of oil migration in the mg bulge is primarily from the west to east direction with the strongest filling point located at approximately the mx12 well the north to west direction is an additional filling orientation these indicators show that those paleo oils that had been cracked to pyrobitumens mainly originated from a source kitchen in the western part of the mg bulge a hydrocarbon source kitchen in the northern part of the mg bulge may also have developed but further research on this is needed the recognition of these solid bitumen molecular signatures particularly the consistent results using dbt concentrations and alkyl dbt thermal maturity indicators suggests a potential approach that can be applied to the study of paleo oil reservoirs

organic matter in upper albian marine sediments in the high tatric units central western carpathians related to oceanic anoxic event 1d geochemistry microfacies and palynology abstract a multidisciplinary study of upper albian hemipelagic sediments related to the oceanic anoxic event 1d oae1d from the high tatric units central western carpathians polish part of the tatra mountains was undertaken to characterize organic matter om and to investigate its origin microfacies and palynological records combined with mineralogical and geochemical data from these sediments show the occurrence of both marine and land derived om in the limestone and marl successions whose deposition corresponds to the parathalmanninella apenninica zone in the late albian both types of om were strongly degraded under the oxic conditions that prevailed during the entire time of their deposition the sedimentation of marls with low contents of total organic carbon

structure and tectonics of the northern sierra nevada recent detailed mapping suggests a new working hypothesis for the structure of the northern sierra nevada we propose that pre cretaceous rocks are deformed by a series of eastward directed over thrusts modified by west directed folds and faults the highest and westernmost tectonic unit is the jurassic smartville complex structurally below it there are imbricate thrust slices of jurassic and older ophiolitic and oceanic sedimentary rocks in the central belt and of paleozoic to jurassic sedimentary and volcanic rocks in the eastern belt the paleozoic feather river peridotite separates the eastern and central belts and our hypothesis suggests that both of its margins may be important thrust faults the east directed faults and folds are deformed by northwest trending upright and west vergent folds and reverse faults that control the present outcrop pattern these later structures have so modified the earlier east directed structures that the latter have been recognized only recently an important key to understanding the structure has been the recognition of ophiolitic complexes that can be correlated across major faults and that contain a pseudostratigraphy useful in determining local structures the events recorded by both the east and west directed deformations occurred during callovian through kimmeridgian time and represent the nevadan orogeny our hypothesis of early east directed overthrusts followed by west directed back folding and faulting implies shortening and thickening of the crust during the nevadan orogeny and is consistent with the idea that the northern sierra nevada is the result of a crustal collisional process

ophiolitic thrust nappes in western nevada implications for the cordilleran orogen new field and geophysical evidence from jurassic mafic and ultramafic rocks in western nevada indicate the presence of two major ophiolite complexes tectonically overlying the rocks of the north american continental margin coupled with the existence of jurassic and older island arc marginal basin complexes and overthrust relations in the adjacent sierran klamath region these ophiolitic thrust nappes in nevada support collision models for the middle jurassic deformation the geometry of the observed structures and their relative age relationships suggest that this deformation might have resulted from the collision of the north american continent with a west dipping subduction zone which resulted in ophiolite emplacement and continental underthrusting continued westward motion of north america beneath the allochthonous oceanic terranes during the late mesozoic developed extensive thrust and possible strike slip faulting in the western us cordillera and caused migration of deformation towards the east this eastward propagation of deformation is interpreted to have resulted in the development of the sevier foreland thrust belt of latest jurassic to latest cretaceous age these collisional processes and the geometry of the proposed collision orogen are reminiscent of the alpine type collision belts

alkane and pah depositional history sources and fluxes in sediments from the fraser river basin and strait of georgia canada hydrocarbon data for dated sediment cores from fraser basin lakes and the strait of georgia in canada reveal a pristine pre industrial background that remains unaltered in modern sediments far from human activities these pristine sediments contain polycyclic aromatic hydrocarbons pahs from combustion natural forest and prairie fires and alkanes and pahs from weathering of soils containing vascular plant remains and natural petroleum hydrocarbons and algal production at other locations examined however these natural loadings have been augmented over the past century by hydrocarbons from petroleum the combustion of liquid oil gasoline and solid coal wood fuels and from processing of wood either directly from disturbed land and slash burning or indirectly through pulp mill effluent although contamination is clearest where there are nearby human activities alkane profiles pah distributions and alkane unresolved complex mixtures suggest a widespread contamination from petroleum combustion products from human activities can also be identified although with less source specificity than with the petroleum products regional emissions from anthropogenic combustion processes appear to support modern pah increases within the fraser river basin and there is little evidence of inputs from global emissions principal components analysis using the new centred log ratio normalisation procedure to normalise data discriminates well between pahs entering lakes from runoff or the atmosphere and pah formed diagenetically within lake sediments as well as between combustion and petroleum pahs

the effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleums abstract the distributions of di and trimethylnaphthalenes in two sedimentary sequences from western australia have been examined by capillary gas chromatography and combined gas chromatography mass spectrometry a general decrease was observed in the relative proportions of dimethylnaphthalenes and trimethylnaphthalenes with increasing thermal maturity similar trends were also observed for six crude oils which have very different ratios of ethylcholestane epimers indicating very different thermal histories these results suggest that changes in the relative abundances of certain methyl substituted naphthalenes may be useful indicators of thermal maturity of sedimentary organic matter and the use of a number of isomer ratios is illustrated

lacustrine shales and oil shales from stellarton basin nova scotia canada organofacies variations and use of polyaromatic hydrocarbons as maturity indicators abstract the post acadian stellarton basin is a small pull apart basin in northern nova scotia the coal brook member which is the main focus of this study contains the thickest and most extensive development of oil shales within the late carboniferous stellarton formation bulk and molecular geochemistry indicate that the organic rich oil shales and black shales contain type i ii kerogen with a mixed assemblage of aquatic and terrestrial organic matter that is dominated by the former biomarker evidence indicates that these sediments were deposited under deep anoxic and fresh to brackish water lake conditions organofacies distinctions were made on the basis of several parameters that are independent of maturity and therefore suggest organic matter changes the organofacies identified are the result of water level fluctuations that are climate controlled all of the aromatic compounds evaluated as maturity parameters were seen to experience alterations in proportion to temperature in the form of either depth or geologic age that can be correlated with maturity these alterations are believed to result from changes in molecular composition maturity parameters based on the alkylbenzothiophenic and alkylnaphthalenic compounds are shown to be effective maturity parameters in lacustrine sequences particularly over the higher maturity ranges where standard maturity parameters based on steranes and hopanes are not effective

identification and distribution of chrysene methylchrysenes and their isomers in crude oils and rock extracts abstract chrysene its methylated homologues and their structural isomers are important polyaromatic compounds in crudes oils coals and sediment extracts chrysene benzo a anthracene methylchrysenes and methylbenzo a anthracenes were unequivocally identified in mass chromatograms by comparison with authentic standards and by retention indices reported in the literature the response factors relating those of chrysene and methylchrysenes to internal standards perdeuterated chrysene chrysene d12 and pyrene pyrene d10 were obtained by gc ms analyses of mixture solutions with different concentration ratios the oil families of ordovician reservoirs in the cratonic region of the tarim basin nw china are distinguished by the distribution patterns of chrysene methylchrysenes and their isomers the majority of the oil accumulations and sediment extracts from the middle upper ordovician source rocks are characterized by low concentrations of benzo a anthracene and methylbenzo a anthracenes relative to chrysene and methylchrysenes respectively in contrast some oils with relatively high abundances of benzo a anthracene and methylbenzo a anthracenes were derived from cambrian and lower ordovician source rocks the effect of maturity on the distribution patterns of methylchrysenes in tertiary lacustrine shales from the liaohe basin east china was investigated the 2 1 methylchrysene ratio keeps a nearly constant value with increasing maturity at the low maturity stages and then it abruptly increases corresponding approximately to the onset of intense c 15 hydrocarbon generation this indicates that chrysene and its methylated homologues are useful molecular indicators in petroleum geochemistry

alkane and pah biomarkers as tracers of terrigenous organic carbon in arctic ocean sediments abstract we present the first sedimentary biomarker study encompassing the entire arctic ocean a large data set of organic markers for terrigenous petroleum and combustion inputs alkanes hopanes and steranes parent and alkyl polycyclic aromatic hydrocarbons pahs is examined for patterns in space and time using principal components analysis pca and partial least squares pls biomarker patterns reveal the central arctic ocean basin sediments to be compositionally distinct from those of the mackenzie river beaufort sea and barents sea but similar to those of the laptev sea pah distributions reflected in pah ratios and pca projections demonstrate that arctic ocean sediment is dominated by natural inputs to the extent that anthropogenic combustion pahs are not significant we find only modest changes between the glacial and post glacial sediments for atmospherically transported hydrocarbon biomarkers while particle associated biomarkers were captured strongly at basin edges during the glacial period and much more evenly transported across basins during the post glacial period the orders of magnitude decreases in particle associated petrogenic alkanes and pahs in central basins during glacial times coupled with the uniformity of most petrogenic biomarker parameters for most basin and shelf locations reflect a massive reduction in ice transport that makes the margins the most likely source of petrogenic material for the pleistocene holocene central arctic basins the proximity of large coal deposits of various maturity levels along the lena river the overlap in pah and biomarker composition of the laptev sea and surficial sediments from the central arctic ocean and the location of the laptev sea at the origin of the main transpolar drift all point to eroded coals from the lena river laptev sea as the likely source of petrogenic hydrocarbons to the central arctic ocean the ubiquitous presence of allochthonous coal in arctic ocean surface sediments provides a major constraint on the use of petrogenic biomarkers to infer the presence of subsurface petroleum reserves

relationships between kinematics of arc continent collision and kinematics of thrust faults folds shear zones and foliations in the nevadan orogen northern sierra nevada california abstract the mesozoic nevadan orogeny in the northern sierra nevada metamorphic belt california may be attributed to arc continent collision stratigraphic data and macroscopic cross cutting relations suggest successive accretion of two arcs along an active continental margin the younger accretion event involved the early jurassic slate creek terrane which is a 3 5 km thick pseudostratigraphic arc fragment the slate creek thrust an isoclinally folded fault with a subhorizontal median surface carries the slate creek terrane at least 40 km eastward continentward over the pre existing continental margin terrane amalgam no rock units can be correlated across the slate creek thrust which is thus interpreted as an arc continent suture in addition to the slate creek thrust the nevadan orogen includes a major east vergent imbricate thrust set east of and beneath the slate creek thrust and steep west vergent reverse shear zones macroscopic upright folds and steep foliations that overprint and cut the east vergent structures these data suggest a model for the relationships between the kinematics of arc collision and nevadan orogenic structures the slate creek arc terrane accreted by westward partial subduction of the continental margin along the east vergent slate creek thrust the continental margin was imbricated along an east vergent thrust set the structurally higher inactive slate creek thrust suture was deformed by steep west vergent shear zones folds and foliations which may have accommodated shortening of the east vergent thrust sheet this deformation occurred within an active continental margin arc that probably initiated by subduction flip after collision of the slate creek arc this kinematic model is consistent with the structural geometry and chronology of the nevadan orogen while qualitatively maintaining lithosphere scale strain compatibility this model has implications for problems related to emplacement of large crystalline thrust sheets displacements beneath and at the margins of shortened crustal segments and interaction of oppositely verging structures the nevadan orogen is a slate belt and the structural plate tectonic model presented for the nevadan orogeny may be testable in slate belts of other orogens

geochemical evaluation of aliphatic and aromatic hydrocarbons in palaeogene source rocks from the latrobe group gippsland basin australia abstract twenty seven hydrocarbon source rocks from the proteacidites asperopolus malvacipollis diversus and lygistepollenites balmei biozones palaeogene latrobe group in the gippsland basin were analysed using gas chromatography mass spectrometry based on the molecular geochemistry of the aliphatic and aromatic fractions together with bulk geochemical data including rock eval pyrolysis and total organic carbon contents the thermal maturity palaeoenvironments and organic matter source of these palaeogene samples were systematically evaluated the results provide a useful comparison with those from upper cretaceous source rocks in the gippsland basin jiang and george 2018 2019 similar to the upper cretaceous rocks the aliphatic hydrocarbons in the paleogene samples are mainly comprised of n alkanes isoprenoids terpanes hopanes and steranes the aromatic hydrocarbons are dominated by naphthalene phenanthrene anthracene fluorene dibenzofuran dibenzothiophene and their alkyl homologues other aromatic hydrocarbons detected include land plant derived compounds e g retene methylretenes cadalene simonellite etc and combustion derived compounds e g chrysene pyrene picene benzo b fluoranthene benzo a anthracene etc these 4 to 6 ring polycyclic aromatic hydrocarbons are more abundant in the paleogene samples compared to the upper cretaceous rocks biomarker and aromatic hydrocarbon distributions indicate that the proteacidites asperopolus and malvacipollis diversus samples are immature or are in the early stage of the oil generation window while the lygistepollenites balmei samples correspond to the low maturity to mature stage the samples were all deposited under sub oxic to oxic conditions in fresh water with low salinity possibly in a lacustrine depositional environment the organic matter inputs are from plankton algae and higher land plants but are dominated by organic matter with a terrigenous origin

a plate tectonic model for late jurassic ophiolite genesis nevadan orogeny and forearc initiation northern california recently published age and structural data allow the reconciliation of previously conflicting models for late jurassic genesis of the josephine smartville and coast range ophiolites and the nevadan orogeny in the klamath mountains and sierra nevada the resulting model is consistent with the mode of initiation location and geometry of the great valley forearc basin and with the lack of a significant forearc basin west of the klamath mountains the coast range ophiolite formed by backarc spreading west of an east facing intraoceanic arc soon thereafter a remnant arc was calved off the west side of this arc and the smartville ophiolite formed by backarc interarc spreading during this time the sierran phase of the nevadan orogeny began as the intraoceanic arc encountered the west facing continental margin arc of north america an east west trending calcalkaline dike swarm in the sierra nevada foothills may mark the trajectory of the colliding arcs at the initiation of the collision simultaneously a new subduction zone was initiated west of the collision suture zone and this new trench propagated southward thus trapping the coast range ophiolite in the new forearc area south of the klamath area intense deformation in the sierran region resulted from this collision and both magmatic arcs became inactive as the last remnant of intervening oceanic crust was subducted continued westward relative movement of the north american arc was permitted north of the sierra nevada owing to the lack of a colliding intraoceanic arc the result was the westward rifting of the continental margin arc by intraarc spreading which formed the josephine ophiolite in the klamath area the klamath phase of the nevadan orogeny resulted from contraction of the west facing intraoceanic arc and josephine backarc basin beneath the continental margin basal sediments of the great valley forearc basin were derived primarily from the sutured arc ophiolite terranes and were deposited on top of the coast range ophiolite the southern edge of the klamaths and the western side of the sierra nevada a new late mesozoic magmatic arc was superposed across the previously accreted terranes and formed the primary sediment source for the cretaceous forearc basin

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

variations of concentration and composition of polycyclic aromatic hydrocarbons in coals in response to dike intrusion in the huainan coalfield in eastern china abstract although extensive studies have been conducted on coals influenced by igneous intrusion the changes of concentration and composition of polycyclic aromatic hydrocarbons pahs in coals responding to this kind of geological rapid heating are largely unknown in the present study thirteen coal samples including unaltered coal thermally altered coal and a dike coal contact sample were collected along a transect approaching an igneous dike intrusion from the no 3 coal seam of the zhuji coal mine in huainan coalfield china these samples represent a broad range of coal ranks ranging from high volatile a bituminous to anthracite vitrinite reflectance ro profiles indicate a progressive increase in ro value from ambient levels of 0 87 1 02 to 5 16 and include an alteration occurring out to 3 6 m from the dike bulk chemical composition from proximate and ultimate analyses shows the typical trend with distance from the dike the total amount of extractable pahs pah35 us epa priority pollutant pahs pah16 and carcinogenic pahs pah8 range from 3 4 81 1 g g 2 5 28 7 g g and 0 7 16 9 g g respectively pah concentrations vary regularly with coal rank reaching a maximum in low volatile bituminous coal 1 62 ro located 3 5 m from the dike this rank is higher than reported for coals not affected by contact metamorphism contact metamorphism has a dramatic effect on the coalification process and results in a different relationship between the pah maximum concentration and coal rank the igneous dike intrusion also has a significant effect on pah distributions where the proportions of 4 6 ring pahs decrease toward the coal dike contact and pahs are dominated by those with 2 and 3 rings the thermally altered coals show a decrease in alkylation compared with that of the unaltered coals and the dealkylation process is apparently accompanied by the cross linking reaction of pahs to form a more compact structure of organic macromolecule

determination of thermal maturity and organic matter type by principal components analysis of the distributions of polycyclic aromatic compounds abstract the thermal maturity and organofacies sensitivity of polycyclic aromatic compound pac distributions was explored by examination of the aromatic fractions of solvent extracts from a diverse set of 53 shales coals and kerogen macerals which have undergone either natural or artificial maturation and which represent all three principal sedimentary organic matter om types systematic changes with maturation were observed in the following groups of isomers tri and tetramethylnaphthalenes methyl and dimethylphenanthrenes methyl and dimethyldibenzothiophenes methylpyrenes and methylchrysenes the maturity differences were quantified by mathematical ratios of the relative concentrations of the more thermally stable isomers to the less stable on the basis of theoretical considerations and empirical observations the pac maturity parameters unlike those derived from saturated biomarker stereoisomers are typically effective across the entire oil generation window to compensate for the effects of om type on the maturity parameters they were combined using principal components analysis the resulting first principal component was in good agreement with independent indicators of maturity the relative distributions of c0 c3 alkylphenanthrenes dibenzothiophene methyldibenzothiophenes and methyldibenzofurans were evaluated by a separate principal components analysis the results permitted an independent grouping of the samples by om type and suggested additional simple molecular ratios that allow graphical recognition of om type including the ratio of dibenzothiophenes to dibenzofurans and a ratio using c2 alkylphenanthrene isomers

structural characterization of kerogen in 3 4 ga archaean cherts from the pilbara craton western australia hydrogen lean kerogen atomic h c 0 46 isolated from the 3 4 ga strelley pool chert in the north pole area pilbara craton western australia were studied by vibrational spectroscopy fourier transform infrared ftir spectroscopy and raman spectroscopy nuclear magnetic resonance spectroscopy solid state 13 c nmr spectroscopy catalytic hydropyrolysis followed by gas chromatography mass spectrometry hypy gc ms and isotope ratio mass spectrometry irms the kerogen occurs in sedimentary rocks as clasts and clots deposited together with other detrital materials that are finely disseminated throughout a chert matrix the bulk kerogen 13 c values range from 28 3 to 35 8 solid state 13 c nmr spectroscopy and ftir spectroscopy reveals that the kerogen is highly aromatic fa varying from 0 90 to 0 92 and contains only minor aliphatic carbon or carbon oxygenated c o functionalities the raman carbon first order spectra for the isolated kerogens are typical of spectra obtained from disordered sp 2 carbons with low 2 d ordering biperiodic structure the implications of the raman results show low 2 d ordering throughout the carbonaceous network indicate the incorrect usage of the term graphite in the literature to describe the kerogen or carbonaceous material in the warrawoona cherts hydropyrolysates contain aromatic compounds consisting of 1 ring to 7 ring polycyclic aromatic hydrocarbons which were covalently bound into the kerogen as well as alkanes linear branched and cyclic which were most probably trapped in the microporous network of the kerogen these pahs have mainly c1 and c2 alkylation while c3 substitued aromatics are low in abundance and do not show a high degree of branched alkylation for the first time we have shown a correlation between elemental analysis h c atomic ratios raman spectroscopic parameters id1 ig id1 id1 ig and la and the degree of alkylation of bound polyaromatic molecular constituents generated from hypy for archaean kerogens similarities in molecular

origin and emplacement of ophiolites ever since their recognition ophiolites have been a source of controversy although all workers have agreed upon their importance a number of conflicting schools of thought have become unified in the interpretation of ophiolite complexes as fragments of oceanic crust and mantle formed at spreading centers an expanded version of the penrose ophiolite definition is proposed herein called the ophiolite association taking into account rocks which bear upon the origin and significance of ophiolite complexes an ideal ophiolite association includes the following units from bottom to top 1 a crystalline basement and shallow water sedimentary sequence 2 a tectonic unit of thrust slices of continental margin and rise and abyssal sediments and or melange 3 a metamorphic unit as much as a few hundred meters thick generally with higher grade rocks over lower grade ones 4 ultramafic tectonite unit composed dominantly of multiply deformed peridotite dunite and minor chromitite 5 a cumulate complex ultramafic at the base grading to mafic or intermediate at the top 6 a noncumulus unit of varitextured gabbro and minor trondhjemite 7 a sheeted dike complex 8 an extrusive section of massive and pillowed flows and intercalated sediments 9 an abyssal or bathyal sediment sequence which may include radiolarian chert red pelagic limestone metalliferous sediments breccias and or pyroclastic deposits and 10 postemplacement deposits of laterite reef limestone or shallow marine or subaerial sediments this expanded ophiolite association allows greater precision in inferring original origin and emplacement some ophiolite complexes particularly in the tethys herein designated tethyan type exhibit units 1 2 3 and 4 whereas others particularly in the cordilleran belt herein termed cordilleran type lack units 1 2 3 and in places 4 the emplacement of the former probably occurred during collision of a passive margin with a subduction zone or incipient subduction zone emplacement of the cordilleran type generally is not clear cut the nature of the spreading center which produced a given ophiolite is indicated more clearly by the presence or absence of units 5 9 than by chemistry or mineralogy some ophiolite complexes lack complete sections and may have formed along transform faults others contain volcanic pyroclastic deposits instead of pelagic sedimentary sequence and probably formed within or near an arc several ophiolite complexes may have originated by conversion of a transform fault into a subduction zone such conversion may result from normal plate evolution or from major plate reorganization major times of ophiolite emplacements appear to correspond with global plate reorganizations

aromatic hydrocarbon biomarkers in terrestrial organic matter of devonian to permian age abstract this paper presents the results of a detailed study on the occurrence and distribution of alkylnaphthalenes and alkylphenanthrenes in 39 coal and sediment samples from the late palaeozoic containing predominantly terrestrial organic matter most of the samples represent the euramerian flora realm and originate from locations beyond the variscan front in eastern northern and central europe i e especially england and the moscow basin the samples are of relatively low maturity 0 32 to 1 80 rr and consist mainly of mixtures of type iii and ii kerogen quantification of the c0 to c4 naphthalenes and the c0 to c4 phenanthrenes showed that these compound classes were highly abundant in all samples aromatic hydrocarbon maturity parameters in general are in good agreement with measured vitrinite reflectance values 1 2 7 trimethylnaphthalene an assumed diagenetic product of oleanane type biomarkers was present in all investigated samples this observation provides evidence that oleanane type lipids were biosynthesised by organisms predating the evolution of angiosperms or that assumed formation pathways for 1 2 7 trimethylnaphthalene are insecure 1 2 8 trimethylphenanthrene was significantly enriched in samples from the permian and the one sample from the devonian investigated in this study the precursor s of 1 2 8 trimethylphenanthrene therefore may have been produced by organisms which were least abundant in the carboniferous depositional environments represented by our samples

high resolution geochemistry of volcanic ash highlights complex magma dynamics during the eyjafjallajokull 2010 eruption the april to may 2010 eruption of eyjafjallajokull iceland volcano was characterized by a large compositional variability of erupted products to contribute to the understanding of the plumbing system dynamics of this volcano we present new empa and la icp ms data on groundmass glasses of ash particles and minerals erupted between april 15 and 22 the occurrence of disequilibrium textures in minerals such as resorption and inverse zoning indicate that open system processes were involved in determining the observed compositional variability the variation of major and trace element data of glasses corroborates this hypothesis indicating that mixing between magma batches with different compositions interacted throughout the whole duration of the eruption in particular the arrival of new basaltic magma into the plumbing system of the volcano destabilized and remobilized magma batches of trachyandesite and rhyolite compositions that according to geophysical data might have intruded as sills over the past 20 years beneath the eyjafjallajokull edifice two mixing processes are envisaged to explain the time variation of the compositions recorded by the erupted tephra the first occurred between basaltic and trachyandesitic end members the second occurred between trachyandesite and rhyolites least squares modeling of major elements supports this hypothesis furthermore investigation of compositional histograms of trace elements allows us to estimate the initial proportions of melts that interacted to generate the compositional variability triggered by mixing of trachyandesites and rhyolites

geochemical study on a well in the western canada basin relation of the aromatic distribution pattern to maturity of organic matter abstract thirty one rock samples from a western canada basin well have been analysed for aromatics using glass capillary gas chromatography with simultaneous flame ionization and sulfur selective flame photometric detection a uniform aromatic distribution pattern with a marked predominance of di and tricyclic aromatic hydrocarbons was observed throughout a depth interval of 3000 meters comprising cretaceous and jurassic sediments the very high relative abundance of sulfur aromatics at two narrow intervals in the triassic and mississippian is attributed to a major change in facies gradual changes with increasing depth have been observed for a series of compound ratios which had been calculated from the isomers of methyl and dimethylphenanthrene and their parent compounds these changes reflect the increasing thermal maturation of the sedimentary organic matter a methylphenanthrene index mpi has been introduced which exhibited a very good correlation with vitrinite reflectance data the mpi is the first maturity parameter which is based on a series of aromatic hydrocarbons this hydrocarbon internal maturity parameter permits the recognition and definition of maturity levels in extracts which can be compared to the maturity e g vitrinite reflectance of source rocks

aliphatic and aromatic biomarkers from gondwanan sediments of late ordovician to early devonian age an early terrestrialization approach abstract twenty one core samples of late ordovician to early devonian age from sections in southern tunisia north african platform gondwana and containing marine and terrestrial organic matter with microbial input were investigated to link the aliphatic and aromatic hydrocarbon distributions with the terrestrial and marine palynomorph content e g acritarchs prasinophytes chitinozoans cryptospores and trilete spores in addition to several biomarkers of algal bacterial origin long chain n alkanes that might be derived from land plants as well as the terrestrial diterpane norabietane were found several land plant derived biomarkers such as retene cadalene simonellite tetrahydroretene and c19 isohexylalkyl naphthalene were observed in the aromatic fractions while these terrestrial biomarkers could be clearly recognized in the middle silurian lower devonian samples their presence in the upper ordovician lower silurian sediments is more doubtful because of much lower relative abundances the land plant biomarkers show a fairly good correlation with the occurrence and abundance of cryptospores and trilete spores derived from bryophytes and tracheophytes which covered the emerged areas around the ghadamis basin during the silurian and devonian the early tracheophytes e g cooksonia lycophytes and zosterophylls are therefore suggested as a new terrestrial source for most of the saturated and aromatic biomarkers found in sediments of middle silurian to early devonian age

biomarker distributions in crude oils and source rocks from different sedimentary environments abstract the saturated and aromatic hydrocarbons from a significant number of oils and source rocks derived from terrestrial and marine organic matter have been analysed by gc and gc ms results show that certain classes of biomarkers including bicyclic sesquiterpanes tricyclic terpanes pregnanes methylsteranes rearranged steranes hopane sulfides benzohopanes long chain alkylbenzenes and pentacyclic triterpanes can be used to distinguish differences in source input and or depositional environments variations in the distributions of the naphthalenes phenanthrenes fluorenes dibenzofurans dibenzothiophenes naphthobenzothiophenes and triaromatic steroid hydrocarbons may also reflect disparities in source input or sedimentary environments

polygenetic ophiolite belt of the california sierra nevada geochronological and tectonostratigraphic development the assumption that ophiolite sequences are generated at essentially one point in geologic time by the process of sea floor spreading is critical for modern concepts in the tectonics of ophiolites and for topics dealing with their structure and petrology however this assumption has only been verified in a few locations by an integrated geochronological and structural stratigraphic approach many ophiolite sections are reconstructed from structurally disrupted sequences with the idealized ocean floor model in mind such reconstructions are prone to error without adequate age control on each of the reconstructed fragments this is a significant problem in structurally complex regions where more than one generation of ophiolite may be present in this paper new pb u zircon ages are presented for key locations along a 375 km segment of the western sierra nevada ophiolite belt these age data are combined with structural stratigraphic observations and published ages and significant tectonic implications for the ophiolite belt emerge three different ophiolitic assemblages are recognized with igneous ages of about 300 200 and 160 m y b p rocks of the 300 m y assemblage are in a completely disrupted array of metamorphic tectonite slabs and serpentinite matrix melange fragments of upper paleozoic seamounts occur in association with the ophiolitic melange and together these assemblages constitute the basement framework for the western sierra pb u and k ar isotopic systematics are complex within this framework and indicate a polymetamorphic history systematics in the 200 and 160 m y assemblages are less complex and give tighter igneous age constraints rocks of the 200 m y assemblage are in a semi intact state with only local tectonite and melange zones rocks of the 160 m y assemblage are intact but nevertheless deformed both the 200 and 160 m y assemblages have equivalent age basinal volcanic sedimentary sequences that lie unconformably above the ophiolitic melange basement in each case the basinal sequences locally extend conformably into the upper stratigraphic levels of the age equivalent ophiolite sections these relations along with vestiges of intrusive contacts between the edges of both younger ophiolites and the melange basement indicate that the younger ophiolites underwent igneous formation in proximity to the melange basement the sierran ophiolite belt is considered to have formed by a multistage process initiated by the early mesozoic tectonic accretion of upper paleozoic sea floor in general proximity to the ancient continental margin regional metamorphism and ophiolitic melange resulted this accretionary nucleus became the basement of jurassic age primitive volcanic arc terranes which underwent rifting episodes during the production of the 200 and 160 m y ophiolites the rifting episodes resulted in the formation of sedimentary basins which were the depositional sites of volcanic sedimentary sequences non volcanic sources for the basinal sedimentary rocks include the melange basement and continental margin terranes contact zones between pre existing basement and the juvenile ophiolitic sequences created during the rifting episodes consist of dynamothermal metamorphic aureoles protoclastic deformation zones and cross cutting dikes such edge zone assemblages are in most localities obscurred or destroyed by superimposed deformations resulting from convergent and perhaps transform motions along basin edges both the 200 and 160 m y basins were destroyed by compressional orogenic episodes shortly after their formational episodes destruction of young ophiolite floored basins may be a common course of events when small oceanic type plates are generated along continental margin environments such tectonic settings are ideal for the emplacement of young ophiolite sheets

geologic and gravity evidence for thrust emplacement of the smartville ophiolite detailed structural relationships at the margins of ophiolites can provide important information about the mode of emplacement of ophiolitic terranes in this study we use geologic mapping and gravity data to determine the structural and tectonic relations between a middle to late jurassic volcanic arc complex the smartville ophiolite block and a pre late jurassic melange terrane in the northern sierra nevada foothills the volcanic arc complex overlies the melange along a complex fault zone although this fault zone is steeply dipping wherever it is observed map patterns suggest that the smartville upper volcanic unit was originally emplaced along a subhorizontal fault that has been subsequently deformed two dimensional interactive computer analysis of gravity data from over 200 stations shows that the smartville upper volcanic unit is a relatively shallow feature with a maximum thickness ranging from 0 5 to 3 km and that it was thrust as a sheet over the previously deformed melange both units were subsequently folded giving rise to the steeply dipping faults observed at the surface recognition of low angle thrusting along the northern margin of the smartville ophiolite block has important implications for the mode of emplacement of the block the most plausible mechanism for the thrusting of this particular oceanic island arc sequence onto the continental margin involves a subduction zone dipping westward beneath the smartville ophiolite block similar to the present day situation in the molucca sea collision zone

tectonic significance of post accretion rifting of a mesozoic island arc terrane in the northern sierra nevada california this paper presents a new interpretation for the tectonic evolution of the smartville complex that forms the western belt of the foothills metamorphic belt in the northern sierra nevada california new geological petrological and geochronological information suggest that the smartville complex may form part of an early jurassic island arc terrane that was probably built on a pre existing oceanic basement inferred oceanic basement is represented by multiply deformed and metamorphosed ophiolitic rocks that crop out in the central belt north and east of the smartville complex that are intruded by numerous lower jurassic dikes of an incipient island arc character lower jurassic volcanic and plutonic rocks of the slate creek and possibly the lake combie complexes in the central belt are interpreted as fragments of the early jurassic arc terrane accretion of the ensimatic arc terrane into the continental margin of north america may have occurred along east vergent thrusting around middle jurassic time and

improved understanding of mixed oil in nigeria based on pyrolysis of asphaltenes abstract crude oil from reservoirs in the onshore niger delta is a mixture of low and high maturity charge aromatic biomarkers in these oils such as alkylphenanthrenes and alkylnaphthalenes show relatively high thermal maturity whereas the saturated sterane and hopane biomarkers indicate lower maturity close to the peak of the oil window the high predicted maturity of the crude oils based on alkylphenanthrene and alkylnaphthalene indices is probably caused by mixing of high maturity condensate with less mature black oil this correlates with the gas washing phenomenon of studied nigerian oils caused by migrating condensate stream the results of our study indicate that asphaltenes can be used to infer the organofacies of the low maturity petroleum charge in mixed crude oils compositional characteristics of the asphaltene pyrolysates indicate an origin of the related oils from type ii iii or type iii source rock kerogen the n alkyl chain length distributions of the asphaltene pyrolysates predict source rocks that generated high wax paraffinic naphthenic aromatic oils or paraffinic oils the n alkyl chain length of asphaltene pyrolysates changes in proportion to oxicity and the relative input of terrigenous organic matter to the source rock

the josephine ophiolite northwestern california the 157 m y old josephine ophiolite is a complete ophiolite consisting of the following units harzburgite tectonite cumulate ultramafics cumulate gabbro interlayered with cumulate ultramafics cumulate gabbro high level gabbro and diorite a 1 5 km thick sheeted dike complex and 0 4 km of pillow lava and breccia the ophiolite is conformably overlain by the galice formation consisting of a thin siliceous pelagic sequence overlain by a thick sequence of turbidites having both volcanic arc and continental margin sources the ophiolite and overlying galice formation were intruded by numerous 150 to 151 m y old calc alkaline dikes and sills followed shortly by deformation and regional metamorphism under conditions of prehnite pumpellyite to lower greenschist facies the josephine peridotite makes up the base of the ophiolite and covers 800 km2 it is an alpine type peridotite that represents upper mantle material and the residue of partial melting ultramafic rocks overlying the josephine peridotite are olivine spinel clinopyroxene cumulates that grade upward into clinopyroxene and orthopyroxene olivine plagioclase cumulates and finally to clinopyroxene plagioclase cumulates high level gabbros and diorites are characterized by highly variable textures complex intrusive relationships strongly zoned plagioclase and abundant mafic dikes plagiogranites occur at this level as dikes small intrusions and screens between mafic dikes but they are rare the sheeted dike complex consists of mafic dikes averaging 0 6 m in thickness chilled margins are locally well preserved and many of the dikes have been split and intruded by younger dikes resulting in half and marginless dikes the dike complex is composed of 100 sheeted dikes near the center but contains gabbro screens near the base and pillow lava and breccia screens in its upper parts the dikes are inclined at 40 to bedding after correcting for folding and are inferred to have been rotated shortly after formation the extrusive sequence consists predominantly of pillow lavas but contains abundant pillow breccias and some massive lavas some of the breccias formed as talus deposits whereas others are graded and matrix supported indicating transport and redeposition possibly in an area of rugged submarine topography the dikes and lavas have geochemical affinities to island arc tholeiites but are in some aspects transitional to mid ocean ridge basalts the dikes and lavas are cogenetic with the underlying plutonic sequence as indicated by similarity in crystallization sequence contradictory intrusive relationships between sheeted dikes and high level plutonic rocks and lack of diabase dikes in the lowermost cumulates and harzburgite the upper portions of the ophiolite were hydrothermally metamorphosed at the spreading center resulting in downward changes in mineralogy texture and 18o in addition metalliferous sediments and massive sulfides that occur overlying and within the pillow lavas probably were formed by precipitation from thermal springs a geothermal gradient of 250 350 c km is inferred from mineral assemblages on the basis primarily of its regional setting the ophiolite is inferred to have formed in a back arc basin in particular it is within a thrust sheet sandwiched between a coeval magmatic arc complex and a slightly older arc complex remnant arc this interpretation is consistent with abundant volcanic arc detritus in graywackes overlying the ophiolite the island arc magmatic affinities of the lavas and dikes may be the result of formation of the ophiolite during the earliest stages of back arc spreading

the emplacement and fault history of the coolac serpentinite lachlan fold belt southeastern australia abstract the tumut synclinorial zone located in the lachlan fold belt southeastern australia forms a fault bounded belt of early silurian volcanics and flyschoid metasediments of the tumut trough the mooney mooney fault system containing an extensive ultramafic belt known as the coolac serpentinite forms the eastern margin of the trough the ultramafics together with mafic volcanics and intrusive grabbroic rocks have been previously interpreted as early palaeozoic oceanic crust dismembered and obducted during late silurian deformation of the silurian trough sequence recent work however has unravelled a more complex history involving several periods of movement the ultramafics and early silurian volcanics are intruded by early silurian gabbro and syn kinematic late silurian granodiorite these intrusive relationships indicate that the ultramafic rocks were present in approximately their present structural position prior to deformation of the trough sequence the ultramafics therefore cannot represent early silurian oceanic crust obducted during the late silurian deformation they probably represent either early silurian or cambrian ordovician mantle derived material emplaced within a strike slip fault zone during early silurian oblique extension

alkylated phenanthrene distribution in artificially matured kerogens from kimmeridge clay and the brent formation north sea abstract kerogen and extractible organic matter from immature kimmeridge clay and brent coal were heated at different temperatures 270 500 c under conditions to mimic natural maturation aromatic fractions have been examined for their phenanthrene compound distribution phenanthrene indices based on methylphenanthrenes mp and dimethylphenanthrenes dmp exhibit very sensible changes in the applied temperature range however at high temperatures about 450 c and more possible thermal degradation of phenanthrene compounds produces a decrease in the values of the indices experimental data obtained in this study are compared and discussed with data obtained on thermal evolution performed on total rocks vitrinite reflectance values measured on artificially matured coals are also tentatively correlated with phenanthrene ratios theoretical thermodynamic calculations on mp compounds confirm also the relative thermal stability of the individual isomers

organic geochemistry and petrology of oil source rocks carpathian overthrust region southeastern poland implications for petroleum generation abstract the organic matter rich oligocene menilite black shales and mudstones are widely distributed in the carpathian overthrust region of southeastern poland and have excellent hydrocarbon generation potential according to toc rock eval and petrographic data extractable organic matter was characterized by an equable distribution of steranes by carbon number by varying amounts of 28 30 dinor hopane 18 h oleanane and by a distinctive group of c24 ring a degraded triterpanes the menilite samples ranged in maturity from pre generative to mid oil window levels with the most mature in the southeastern portion of the study area carpathian petroleum samples from campanian oligocene sandstone reservoirs were similar in biomarker composition to the menilite rock extracts similarities in aliphatic and aromatic hydrocarbon distributions between petroleum asphaltene and source rock pyrolyzates provided further evidence genetically linking menilite kerogens with carpathian oils