provenance and tectonic settings of permian turbidites from the beishan mountains nw china implications for the late paleozoic accretionary tectonics of the southern altaids the beishan orogenic belt which connects the tianshan suture on the west and solonker suture on the east contains key evidence for the termination time of the southern altaids critical for evaluating different controversial tectonic models are permian marine volcaniclastic arenites in the liuyuan and heishankou areas which are dominated by greywackes and lenticular pebbly litharenites that contain grading groove marks and erosional bases which provide evidence of turbidity action sandstones from the liuyuan section are dominated by angular basaltic andesitic and feldspar fragments but sandstones from the heishankou section mainly consist of andesitic and felsic volcanic fragments these relations suggest derivation from two different sources major element compositions suggest that the source rocks of the heishankou litharenites were more sio2 rich than those at liuyuan sandstones at heishankou are characterized by lower ni co cr v and slightly higher th and la contents than those at liuyuan this indicates that the litharenites in the liuyuan and heishankou areas were derived from intermediate mafic and intermediate felsic source rocks respectively tectonic setting discrimination plots suggest that the liuyuan sandstones were deposited as detritus from an oceanic island arc but the heishankou sediments from an andean continental margin our petrological and geochemical data from these two types of permian turbidites suggest that an arc continent collision took place in the early permian and this is consistent with the permian termination of the southern altaids

bicadinanes and related compounds as maturity indicators for oils and sediments abstract biomarker maturity indices have proven useful in petroleum exploration to assess the thermal maturity of oils and sediments however their application to deltaic petroleum systems is often hindered by source and diagenetic interferences recently we have described several new maturity indices based on the catagenetic products of the plant biopolymer polycadinene these indices should be largely immune to biochemical effects during diagenesis since little microbial activity will remain at temperatures sufficient to dissociate the polymer here we report changes in five polycadinene related maturity indices through a marine fluvio deltaic depositional sequence in the south sumatra basin indonesia the results are compared with the maturity required for oil generation as estimated by kinetic modelling and with conventional maturity indicators such as sterane epimerisation and the methyl phenanthrene index the data confirm that the polycadinene indices are less subject to source and diagenetic interferences than those based on the sterane and aromatic hydrocarbon distributions values for several of the indices have also been measured for 17 tertiary oils from southeast asia papua new guinea new zealand and australia contrary to an earlier report the bicadinane maturity indicator bmi 1 continues to change into the oil window and hence may be useful in ranking the relative maturity of oils as well as sediments the bmi 1 values for two oils having unusually low sterane maturities are normal leading us to question whether the low sterane maturity of many tertiary age oils is due to their source rocks having been heated more rapidly than those of older oils

biomarkers of oligocene lacustrine source rocks beibuwan song hong basin junction offshore northern vietnam abstract highly oil prone source rocks containing sapropelic type i and mixed types i and iii kerogen are found in 233 m of the 500 m deep fully cored enreca 3 well drilled on bach long vi island located at the junction between the beibuwan and the song hong basins offshore northern vietnam the cored succession is made up entirely by oligocene deep lacustrine deposits the origin of the organic matter om in 62 samples is evaluated on the basis of gas chromatography mass spectrometry gc ms and gc ms ms om in 55 samples is sourced primarily from lacustrine organisms and contains abundant 4 methylsteranes tetracyclic polyprenoids tpp and lycopane and no markers for marine organic matter the proportion of triterpanes derived from angiosperms is low in most saturated fractions and only traces of gymnosperm diterpanes are detected in contrast all aromatic fractions have a high proportion of compounds having an origin from both gymnosperms and angiosperms very high concentrations of hopanoids in both fractions suggest significant bacterial alteration of the original om most samples have a high concentration of rare c31 diaromatic 8 14 secohopanes with a fluorene moiety low pristane phytane pr ph ratios indicate that anoxic suboxic bottom water conditions existed during om accumulation the presence of carotane gammacerane and traces of arylisoprenoids could indicate a stratified water column om in a few samples with lower than average hydrogen index hi is mainly of terrestrial origin with a higher proportion of c29 steranes diterpanes and oleanoids and lower concentrations of both saturated and aromatic hopanes higher pr ph a higher c34 isohopane ratio ihr34 and a lower homohopane index hhi indicate that this low hi om was originally deposited under more oxic conditions and subsequently transported to deeper water low sterane and hopane isomerization ratios show that no samples have reached the oil window some novel maturity parameters for immature lacustrine samples are proposed

thermal alteration of terrestrial palynomorphs in mid cretaceous organic rich mudstones intruded by an igneous sill newfoundland margin odp hole 1276a most approaches used to reconstruct thermal alteration of sediments necessitate advanced relatively expensive analytical techniques we have evaluated the fidelity of a less costly relatively simple approach of visually assessing sporomorph colours to determine thermal alteration the sporomorph based thermal alteration estimates were compared to vitrinite reflectance data from the same samples as study material we selected a succession of mid cretaceous albian organic rich clay and siltstones intruded by a diabase sill that was recovered from ocean drilling program odp hole 1276a off newfoundland six sporomorph groups sg each consisting of morphologically well defined easily identifiable constituents with long stratigraphic ranges were individually evaluated for their thermal alteration signals these groups are 1 leiotrilete spores of the genera biretisporites cyathidites deltoidospora dictyophyllidites gleicheniidites and leiotriletes sg 1 subdivided into three subgroups sg 1a sg 1b and sg 1c with sporoderm thicknesses 1 5 m respectively 2 trilete rugulate spores of the genera camerozonosporites and lycopodiacidites sg 2 3 trilete striate spores of the genera appendicisporites cicatricosisporites and plicatella sg 3 and 4 the gymnosperm pollen taxon classopollis torosus sg 4 sporomorph colours were determined using munsell colour standards under reproducible optical conditions to minimize the potential influence of reworked specimens on the dataset only the lightest 50 of all counted specimens per sporomorph group were evaluated for their thermal alteration signals the thermal alteration estimates from all sporomorph groups yield an internally consistent picture that is compatible with vitrinite reflectance data from the same samples they indicate that downhole thermal alteration does not increase until 20 m above the igneous sill a steep rise occurs only at 4 23 m above the sill and thermal alteration peaks in the sample closest 2 17 m to the sill however the different sporomorph groups exhibit varying degrees of fidelity with respect to deciphering thermal alteration factors influencing the precision of the thermal alteration signal include sporoderm thickness character of surface ornamentation resistance to reworking and abundance in the sample material highest correlations with vitrinite reflectance data are observed for the thermal alteration values from sg 1b r 0 82 sg 3 r 0 80 and sg 4 r 0 80 hence these groups are best suited for a sporomorph based approach to reconstructing the thermal history of sediments the highest correlation coefficient with vitrinite reflectance data is registered for sg 1b the subgroup with the least variability of sporoderm thickness and the highest abundance in the sample material this indicates that the study of morphologically similar highly abundant specimens with strongly constrained sporoderm thickness variations yields the best results for the reconstruction of thermal alteration

the late archean history of the wyoming province as recorded by granitic magmatism in the wind river range wyoming abstract the wyoming province a small ca 500 000 km 2 archean craton is the most southwestern of the archean provinces in north america it is composed primarily of late archean potassium rich granitic rocks in contrast to many other archean provinces rocks of tonalite trondhjemite affinity are rare over most of the province and are restricted to rocks older than 2 8 ga field petrologic geochemical and isotopic study of the late archean granites exposed in the wind river range have allowed us to identify at least four periods of potassic calc alkalic magmatism at 2 8 2 67 2 63 and 2 55 ga granitic rocks of these ages appear to be widespread across the wyoming province the oldest calc alkalic granites of the wind river range emplaced at ca 2 8 ga appear to be derived predominantly from pre existing crust however nd isotopic data suggest that these granites cannot be the product solely of partial melting of older tonalitic gray gneisses during at least two other periods of plutonism at 2 67 and 2 63 ga generation of the wind river range batholiths involved the incorporation of substantial amounts of isotopically juvenile material either from depleted mantle or young continental crust the information presented below as well as data available from elsewhere in the wyoming province is interpreted to suggest that the wyoming province unlike other archean cratons is not composed of a tectonic amalgamation of smaller exotic terranes although the wyoming province did experience crustal addition in archean time it was not by lateral accretion but by incorporation of mantle derived melts into large granitic batholiths

identification of bicadinanes in jurassic organic matter from the eromanga basin australia cis cis trans and trans trans trans bicadinanes were identified in a jurassic crude oil and two jurassic rocks from the eromanga basin australia after the branched and cyclic alkane fractions had been enriched in bicadinanes using ultrastable y molecular sieves these biomarkers have previously been reported only from angiosperms and their occurrence in jurassic samples may indicate the early evolution of flowering plants in this basin

triterpane and sterane biomarkers in the ya13 1 condensates from qiongdongnan basin south china sea triterpanes and steranes in condensates from the ya13 1 gas field qiongdongnan basin were monitored the ya13 1 condensates have unusual biomarker distributions dominated by terpanes and steranes derived from higher plants anomalously abundant 1 got oleanane and remarkably abundant bicadinanes are present in the ya13 1 condensates whereas the 17alpha hopane contents are extremely low taraxastane and significantly abundant 17alpha diahopanes occur in the condensates in addition a number of unknown c 29 and c 30 pentacyclic triterpanes including previously unreported compounds were detected in the condensates some of which are significantly abundant the unknown compounds may be terrestrial biomarkers c 29 homologues are relatively predominant among the regular and rearranged steranes the diasterane concentrations are markedly higher than those of regular steranes the maturity of the ya13 1 condensates is relatively high at the peak to late oil generation stage corresponding to 0 85 1 10 ro based on sterane and terpane and including bicadinane maturity parameters i e t t 1 r and 2t r bicadinane ratios the above maturity assessment result is different from that based on diamondoid maturity parameters ro 1 60 1 70 org geochem 25 1996 179 which can be explained by a contribution of hydrocarbons from two sources at different depths the ya13 1 condensates were probably generated from the yacheng and lingshui coal bearing source rocks buried both in the qiongdongnan basin 3400 5000 m and in the yinggehai basin 5000 m the possible contribution of lower maturity hydrocarbons from the yacheng and lingshui formations 3400 4100 m in the qiongdongnan basin to the ya13 1 gases and condensates should not be neglected c 2003 elsevier science b v all rights reserved

sterane isomerisation and moretane hopane ratios in crude oils derived from tertiary source rocks the extent of sterane isomerisation reactions and the moretane hopane ratios of 234 crude oils taken world wide from a wide variety of source rocks of differing geological ages have been measured this data indicates that in 78 crude oils derived from tertiary source rocks sterane isomerisation reactions as determined by the 20s 20s 20r ration of the c29 5 h 14 h 17 h normal steranes and the c29 iso iso normal ratio iso 5 h 14 h 17 h are mainly incomplete and sometimes considerably so in addition the same crude oils have 17 h 21 h moretane 17 h 21 h hopane ratios which are significantly greater predominantly in the range 0 10 0 30 than those of crude oils derived from older mature source rocks mainly less than 0 1 this data for crude oils lends support to the hypothesis proposed by mackenzie and mckenzie 1983 for source rock extracts that the time temperature constraints of sterane isomerisation reactions are such that the time available for isomerisation in tertiary sediments is generally insufficient despite generation of crude oil at relatively high temperatures an alternative hypothesis is that the incomplete sterane isomerisation of tertiary crude oils may be due to generation of these crude oils from their deltaic land plant containing source rocks under low heating conditions a third hypothesis proposes that the tertiary crude oils may have picked up the incompletely isomerised steranes from immature sediments during migration although possible in particular instances such a mechanism does not appear to be generally applicable since in that case the phenomenon would then appear to be restricted to the tertiary the higher moretane hopane ratios of the tertiary crude oils could suggest that constraints similar to those applying in sterane isomerisation also operate in the conversion of moretane to 17 h hopane

the effect of maturity on the relative abundances of cadalene and isocadalene in sediments from the gippsland basin australia abstract two sedimentary sequences from the gippsland basin australia have been analysed for cadelene and 3 isopropyl 1 6 dimethylnaphthalene isocadalene the relative abundance of these compounds changes with increasing depth maturity of the sediments and is associated with an increase in the abundance of 1 6 dimethylnaphthalene relative to other dimethylnaphthalene isomers these changes have been attributed to dealkylation and isomerization reactions of cadalene in the sediments because analogous changes have been demonstrated in laboratory heating experiments in which cadalene was converted into a mixture containing mainly 1 6 dimethylnaphthalene and isocadalene when heated in the presence of aluminum smectite the ratio of isocadalene and cadalene may be a useful maturity parameter for some sediments and crude oils which contain these compounds

pentamethylnaphthalenes and related compounds in sedimentary organic matter abstract the isomeric pentamethylnaphthalenes pmns 1 2 3 5 6 pmn 1 2 3 5 7 pmn 1 2 3 6 7 pmn and 1 2 4 6 7 pmn have been synthesised characterised and identified in a number of crude oils and sediments ranging in age from proterozoic to tertiary we suggest that 1 2 3 5 6 pmn forms predominantly from the aromatisation of drimanoid precursors via 1 2 2 5 6 pentamethyltetralin when 1 2 3 5 6 pmn was heated in laboratory experiments the proportions of pmns changed in a manner which reflected the relative stability of the isomers the other pmns in sediments are therefore suggested to arise via acid catalysed isomerisation or transalkylation processes a conveniently measured pentamethylnaphthalene ratio pnr 1 2 4 6 7 pmn 1 2 3 5 6 pmn 1 2 4 6 7 pmn has been defined as a maturity parameter in an indonesian sedimentary sequence the values of pnr changed smoothly with increasing depth with values ranging from 0 1 to 0 4 values in crude oils range from 0 15 to 0 85 suggesting a value of approximately 0 15 for the beginning of the oil window

widespread basement erosion during the late paleocene early eocene in the laramide rocky mountains inferred from 87sr 86sr ratios of freshwater bivalve fossils reconstruction of the timing and pattern of exhumation of basement involved uplifts during the laramide is essential to the understanding of the mechanisms of crustal shortening and thickening in the region we use reconstructions of the 87 sr 86 sr ratios of late cretaceous early cenozoic river water from fossil shells in six basins of the rocky mountains contextualized by modern river water sr chemistry studies to trace the erosion of precambrian basement cores in the laramide ranges the 87 sr 86 sr ratios and sr concentration of modern river water in the rocky mountains are controlled by river bedrock lithology weathering of precambrian silicate rocks in the cores of laramide ranges produces high 87 sr 86 sr ratios in highland rivers weathering of paleozoic and mesozoic carbonates along the basin margins reduces the 87 sr 86 sr ratios and increases sr concentration of rivers as they flow basinward lowland rivers that have headwaters in precambrian basement mostly have 87 sr 86 sr ratios 0 711 whereas rivers confined to or with very long reaches in basins have 87 sr 86 sr ratios between 0 709 and 0 711 river water 18 o values do not change in response to changes in catchment elevation our results from fossil shells show that carbonate weathering dominated the river water sr chemistry in the alberta foreland williston and crazy mountains basins and that proterozoic low grade metamorphic carbonates in the belt purcell supergroup were not exposed in the canadian rocky mountains during late cretaceous early paleocene time silicate weathering influenced the sr chemistry of surface waters in the powder river basin during the late paleocene and the washakie basin during the early eocene suggesting precambrian silicate basement rock was extensively exhumed and eroded the observation that precambrian basement was eroded earlier around the powder river basin than around the washakie basin is consistent with a previous study that suggests laramide ranges in northeast wyoming reached high elevation earlier than the ranges adjacent to the sevier thrust belt widespread basement erosion in late paleocene early eocene time was controlled by tectonic exhumation and may have been intensified by the wet and warm global climate

tidal sedimentology and estuarine deposition of the proterozoic big cottonwood formation utah abstract the mesoproterozoic to neoproterozoic big cottonwood formation of north central utah contains some of the oldest known 900 ma examples of cyclic tidal rhythmites despite mild metamorphic overprinting there is excellent preservation of sedimentary structures the thick formation 4 8 km has been previously interpreted as a shallow water intracratonic basin deposit five distinct facies are recognized two quartz arenite facies are dominated by dune meter scale cross bedding recording westward flow but distinguished by different large scale geometries 1 thick tabular bodies 10 20 m thick by 600 m long and 2 channeled beds 0 3 0 3 m thick by hundreds to thousands of meters long channeled beds have scoured bases and coarse grained lags or rip up clasts stacked channel beds form upward fining successions up to 50 m thick three distinct argillite facies contain different structures and cyclicities and are also characterized by color dark laminated argillites contain abundant heterolithic rhythmites with thick couplets up to 1 cm per lamina syneresis cracks flame structures internal truncation scours intraformational blocks clasts and diagenetic pyrite the other two argillite facies commonly occur overlying channelized quartzites in large scale upward fining successions a transitional argillite composed of thin intertidal beds grades upward into mud cracked argillite of massive to weakly bedded intertidal to supratidal beds characterized by wave ripples and abundant mud cracks important diagnostic tidal features recognized in the big cottonwood formation include 1 heterolithic tidal rhythmites 2 current ripples with crests rounded by backflow 3 sigmoidal bundles and 4 abundant clay draped reactivation surfaces other structures that corroborate the tidal interpretation include 1 flaser bedding 2 mud cracks and 3 mud draped wave ripples the sedimentary structures and genetic sequence relationships recognized in this study suggest deposition in a tide dominated estuary the laminated argillites with heterolithic rhythmites indicate subtidal deposition in tidal channels sand filled tidal channels are represented in stacked quartzite beds that grade to transitional argillite and thin successions of mud cracked argillite thicker units of mud cracked argillite may represent deposition in tidal flats with periodic exposure tabular sheet quartzites suggest deposition as sand sheets near the mouth of the estuary our documentation of tidal rhythmites and estuarine deposition suggests previously unrecognized mesoproterozoic to neoproterozoic tidal deposition in north central utah

derivation of s and pb in phanerozoic intrusion related metal deposits from neoproterozoic sedimentary pyrite great basin united states the thick 8 km regionally extensive section of neoproterozoic siliciclastic strata terrigenous detrital succession tds in the central and eastern great basin contains sedimentary pyrite characterized by mostly high 34 s values 11 6 to 40 8 70 exceed 10 51 analyses derived from reduction of seawater sulfate and by markedly radiogenic pb isotopes 207 pb 204 pb 19 2 15 analyses acquired from clastic detritus eroded from precambrian cratonal rocks to the east southeast in the overlying paleozoic section pb zn cu ag au deposits associated with jurassic cretaceous and tertiary granitic intrusions intrusion related metal deposits contain galena and other sulfide minerals with s and pb isotope compositions similar to those of tds sedimentary pyrite consistent with derivation of deposit s and pb from tds pyrite minor element abundances in tds pyrite e g pb zn cu ag and au compared to sedimentary and hydrothermal pyrite elsewhere are not noticeably elevated implying that enrichment in source minerals is not a precondition for intrusion related metal deposits three mechanisms for transferring components of tds sedimentary pyrite to intrusion related metal deposits are qualitatively evaluated one mechanism involves 1 decomposition of tds pyrite in thermal aureoles of intruding magmas and 2 aqueous transport and precipitation in thermal or fluid mixing gradients of isotopically heavy s radiogenic pb and possibly other sedimentary pyrite and detrital mineral components as sulfide minerals in intrusion related metal deposits a second mechanism invokes mixing and s isotope exchange in thermal aureoles of pb and s exsolved from magma and derived from decomposition of sedimentary pyrite a third mechanism entails melting of tds strata or assimilation of tds strata by crustal or mantle magmas tds derived or assimilated magmas ascend decompress and exsolve a mixture of tds volatiles including isotopically heavy s and radiogenic pb from sedimentary pyrite and volatiles acquired from deeper crustal or mantle sources in the central and eastern great basin the wide distribution and high density of small to mid sized vein replacement and skarn intrusion related metal deposits in lower paleozoic rocks that contain tds sedimentary pyrite s and pb reflect 1 prolific jurassic cretaceous and tertiary magmatism 2 a regional substrate reservoir of s and pb in permeable and homogeneous siliciclastic strata and 3 relatively small scale concentration of substrate and magmatic components large intrusion related metal deposits in the central and eastern great basin acquired s and most pb from thicker lithospheric sections

a new paleomagnetic pole for the neoproterozoic uinta mountain supergroup central rocky mountain states usa abstract hematite cemented strata of the neoproterozoic age 800 750 ma uinta mountain group umg provide a new well defined mid neoproterozoic paleomagnetic pole for laurentia thermal demagnetization results and rock magnetic experiments reveal the presence of two discrete magnetizations in umg rocks both magnetizations are carried by hematite the dominant characteristic remanent magnetization chrm is an east directed or antipode shallow positive to negative inclination magnetization that is typically unblocked over a narrow range of high laboratory temperatures between 660 and 680 c the second magnetization exclusively of normal polarity is north to northeast directed and has a moderate to steep positive inclination and probably represents a recent or modern day viscous remanent magnetization the response of umg samples to thermal and chemical demagnetization comparison with previously obtained data from umg rocks in the area results from rock magnetic experiments and the inferred low latitude of laurentia during umg deposition in the neoproterozoic are all consistent with the interpretation that the west or east directed shallow magnetization is a near primary remanence the presence of dual polarities of the chrm with the west directed remanence inferred to be of normal polarity and the east directed of reverse polarity suggests that magnetization acquisition in the umg rocks took place over a sufficient amount of time to average secular variation of the geomagnetic field the mean paleomagnetic pole derived from the inferred primary magnetizations from umg strata 0 8 n 161 3 e 95 4 6 n 9 sampling localities consisting of 79 sites is fully consistent with recently reported results from rocks of mid neoproterozoic age for southwest laurentia which define a tight counterclockwise loop located in the south pacific in the apparent polar wander path for laurentia during the neoproterozoic

occurrence of polycadinene in fossil and recent resins abstract dammars produced by dipterocarpaceae growing in southeast asia are partly composed of a macromolecule with a polycadinene structure this polymer is the precursor of many specific compounds encountered in crude oils and sediment extracts from south asia until recently there was no evidence for a more widespread geographical occurrence of this resinous polymer using different pyrolysis methods it is shown that the polymers present in a resinite from utah usa and in resins contained in resin canals of eocene fossil fruits from germany and england are also polycadinenes the fossil fruits were undoubtedly produced by ancient representatives of mastixioid cornaceae a group of plants which was widespread in the tertiary of europe and north america and which is not related to dipterocarpaceae these findings extend the known occurrence and origin of the sesquiterpenoid type resin polymer it is to be expected that catagenetic products of these resin polymers should be present in oils coals and sediment extracts from areas outside southeast asia

the influence of source rock type chemical weathering and sorting on the geochemistry of clastic sediments from the quetico metasedimentary belt superior province canada abstract the geochemistry of clastic sediments is controlled by at least four factors source rock composition weathering of the source rocks sorting of the weathered detritus and post depositional alteration during diagenesis and metamorphism in order to evaluate the relative importance of these factors major trace and rare earth element contents were determined for distal and proximal clastic turbidites from the archaean quetico metasedimentary belt the degree of metamorphism of the samples ranges from middle greenschist to upper amphibolite facies simple mixing of archaean mafic and acidic rocks of similar composition to those found in the adjacent granite greenstone terrains will account for the tio2 feot mgo cr sc y and hree contents of the clastic turbidites the metasediments are enriched in lree relative to the mafic acidic rock mixing line indicating that the acidic source was enriched in the lree compared to archaean terrains from other parts of the world some quetico turbidites have an additional fe rich source component possibly a chemical sediment incorporated at the time of turbidite slumping cao na2o k2o rb and sr form trends on bivariant plots that are oblique to the mafic acidic rock mixing line and hence cannot be accounted for by simple mixing of the source rocks chemical weathering of feldspars prior to deposition can account for cao na2o k2o rb and sr trends since cao na2o and sr are lost to the weathering solutions and k2o and rb are retained on the product clays the higher na 2 o cao k 2 o na 2 o rb k 2 o and sr cao ratios but lower cao content of the distal samples suggest that they were derived from a bulk sediment that had experienced a greater degree of chemical weathering than the proximal sediments sorting is the factor that most strongly influences the composition of individual samples within the proximal sample group the coarse grained metagraywackes with their higher quartz feldspar and heavy mineral contents are enriched in sio2 cao na2o sr lree zr and hf relative to the fine grained clay rich metapelites metapelites are enriched in tio2 al2o3 feot mgo k2o cr zn sc y hree cs and rb as a result of their higher clay contents thus the use of clastic sediment compositions in determining average crustal compositions e g for the ree can only give satisfactory results when all grain size fractions are sampled in their correct relative proportions the chemical differences observed between the high and low grade samples can be accounted for by source rock type chemical weathering of the source rocks or sorting post depositional element mobility does not appear to be an important factor in determining the composition of the quetico metasediments

tectonic evolution of lower proterozoic rocks uinta mountains utah and colorado rocks of the early proterozoic orogenic system that fringes the archean aged wyoming province are exposed along the uinta fault in the northeastern uinta mountains of utah and colorado exposed here are the red creek quartzite an early proterozoic type miogeoclinal metasedimentary sequence more than 4 km thick and an underlying newly recognized archean gneiss complex more than 2 7 b y old during the hudsonian orogenic period the miogeoclinal sequence was emplaced northward over the archean complex by tectonic translation along a thick mylonite zone in the waning phases of upper amphibolite metamorphism the orogen was disrupted by east trending block faults with several kilometres displacement during initiation of the uinta aulacogen and was buried by more than 7 km of middle proterozoic sediments of the uinta mountain group the middle proterozoic block faults were reactivated with reversed sense of displacement during the laramide uplift of the uinta mountain block

provenance of paleocene eocene red beds from ne iraq constraints from framework petrography the red bed deposits in northern iraq are situated in an active foreland basin adjacent to the zagros orogenic belt bound to the north by the iranian plate thrust over the edge of the arabian plate the red bed successions are composed of alternating red and brown silty mudstones purplish red calcareous siltstone fine to coarse grained pebbly sandstone and conglomerate the red beds in the current study can be divided into four parts showing a trend of upward coarsening with fine grained deposits at the top a detailed petrographic study was carried out on the sandstone units the clastic rocks consist mainly of calcite cemented litharenite with rock fragments volcanic metamorphic and sedimentary quartz and minor feldspar the petrographic components reflect the tectonic system in the source area laterally ranging from a mixed orogenic and magmatic arc in mawat chwarta area to recycled orogenic material rich in sedimentary rock fragments in the qandel area the cretaceous palaeogene foreland basin of northern iraq formed to the southwest of the zagros suture zone and the sanandaj sirjan zone of western iran during palaeogene time deposition of the red beds was caused by renewed shortening in the thrust sheets overlying the arabian margin with uplift of radiolarites qulqula formation resulting in an influx of radiolarian debris in addition to continuing ophiolitic detritus mixed sources including metamorphic volcanic and sedimentary terranes were present during deposition of the upper part of the red beds

trace elements as source indicators in cratonic sediments a case study from the early proterozoic libby creek group southeastern wyoming to understand how grain size and sorting effect trace element distributions in sediments we compare the compositions of closely associated quartzites pelites and glacial diamictites from the 2 ga libby creek group in se wyoming we found similar ree distributions lree enriched negative eu anomalies and that most compositional differences can be explained by variable quartz dilution trace element distributions from mineral separates in a fuchsite quartzite show that fuchsite contains most of the th u ree sc co and ni and controls the whole rock ree distributions zircon contains most of the zr and hf but 5 of the hree in the pelites and 20 in the quartzites other than zr and hf most trace elements in libby creek sediments are chiefly in micas and were probably in clays in the original sediments increased eu anomalies in upper libby creek sediments signal a sudden increase in eu depleted granitoids in sediment sources which reflects late tectonic uplift mixing models favor granite ba

infilling history of a neoproterozoic intracratonic basin nd isotope provenance studies of the uinta mountain group western united states abstract neodymium isotope and selected trace element concentration data were obtained from 27 samples of shales and arkosic sandstones comprising the neoproterozoic uinta mountain group umg in north eastern utah and northwestern colorado to determine the provenance of siliciclastic detritus deposited in this region and to reconstruct aspects of the proterozoic geologic history of the southern margin of the archean wyoming province in the east lobe of the uinta mountains coarse grained components of the jesse ewing canyon formation the oldest recognized formation of the umg have measured nd values of 23 to 28 and were most probably derived from archean basement of the wyoming province to the north fine grained sediment in the southern portions of the jesse ewing canyon formation and shales and quartz arenites from overlying undifferentiated umg all contain at least a component of detritus derived from proterozoic crust in the west lobe the oldest members of the umg the red castle lake gilbert peak and moosehorn lake formations and arkosic arenite comprising the northern portions of the overlying mount watson formation were also derived exclusively from archean sources however as in the east lobe the more mature sandstones that dominate the southern sections of the mount watson formation have isotopic compositions that require a significant proterozoic crust derived detrital component our data support a model in which sedimentary rocks with an archean provenance represent the preserved remnants of alluvial fans marking the northern margin of the basin in which the umg was deposited a source for these sediments within the archean wyoming province is consistent with the high light rare earth element lree and th abundances of finegrained low nd sedimentary rocks given that late archean granitic rocks within the wyoming province have similar trace element characteristics sediments with proterozoic components in both the east and west lobes were apparently deposited from a fluvial system that transported sediment along the basin axis the proterozoic detrital component in these sediments originated either through direct erosion of the colorado province in the neoproterozoic or through erosion of mixed archean and proterozoic crust located to the east of the umg basin that originally formed during the paleoproterozoic accretion of the colorado province to the southern margin of the wyoming craton

another look at rare earth elements in shales linear correlation and mass balance considerations indicate that clays are more important than zircon or other heavy minerals in hosting both light and heavy ree in cratonic shales considering the uniformity of the eu anomaly and ree distributions in cratonic shales it seems likely that detritus is thoroughly mixed during weathering and sediment transport and that the ree patterns in shales reflect the average ree pattern of the sources regardless of the ratio of clays to heavy minerals in the shales shales suspended river loads and near shore marine sediments all have broadly similar ree patterns and reported hree depletions in the latter two groups may reflect incomplete dissolution of heavy minerals during sample preparation ree distributions in shales and suspended river loads determined by inna are similar to those in average upper continent crust and ree distributions in shale averages nasc and paas seem to be reasonably representative of the average composition of post archean upper continental crust

geochemistry of sandstones from the upper miocene kudankulam formation southern india implications for provenance weathering and tectonic setting abstract petrographic major trace and rare earth element compositions of sandstones from the upper miocene kudankulam formation southern india have been investigated to determine their provenance tectonic setting and weathering conditions all sandstone samples are highly enriched in quartz q but poor in feldspar f and lithic fragments l the major element concentrations of these sandstones reveal the relative homogeneity of their source geochemically the kudankulam sandstones are classified as arkose subarkose litharenite and sublitharenite the cia values chemical index of alteration mean value 44 5 for these sandstones and the a cn k diagram suggest their low weathering nature similarly their fe2o3 mgo mean 2 7 al2o3 sio2 0 09 k2o na2o 2 2 ratios and tio2 contents 0 3 are consistent with a passive margin setting the eu eu 0 5 la lu cn 21 la sc 5 9 th sc 1 9 la co 5 7 th co 1 8 and cr th 5 3 ratios support a felsic source for these sandstones chondrite normalized ree patterns with lree enrichment flat hree and negative eu anomaly also are attributed to felsic source rock characteristics for kudankulam sandstones total ree concentrations of these sandstones reflect the variations in their grain size fractions the source rocks are probably identified to be proterozoic gneisses charnockites and granites of the kerala khondalite belt which must have been exposed at least since the late miocene finally the unusual ni enrichment in the kudankulam sandstones unaccompanied by a similar enrichment in cr co and v may be related to either the presence of pyrite in the sandstones or more likely the fractionation of garnet from the source rocks during transportation

the cr th ratio in precambrian pelites from the kaapvaal craton as an index of craton evolution the cr th ratio in precambrian pelites from the kaapvaal craton in southern africa correlates with pelite th sc and co th ratios and appears to monitor changes in source composition it is a more sensitive indicator of provenance than other commonly used ratios including eu eu la yb and th u pelite cr th ratios are controlled most strongly by the effects of local provenance and local tectonics secular decreases in this ratio the most prominent of which occurred at 2 4 2 3 ga in pelites of the kaapvaal craton record rapid uplift exposing granite decreases in the ratio reflect increases in the abundance of komatiite basalt in sediment sources in response to arc collisions rift hotspot volcanism or intracratonic uplift of older greenstones relatively constant cr th ratios appear to require widespread uplift or and efficient sediment mixing during tectonic stability changes in cr th ratio of kaapvaal pelites reflect a complex tectonic history of the craton from about 3 3 ga to 1 8 ga and do not favor single stage cratonization in the late archean

the effect of drainage reorganization on paleoaltimetry studies an example from the paleogene laramide foreland abstract using multiple isotope systems we examine the complex effects of drainage reorganization in the laramide foreland in the context of stable isotope paleoaltimetry strontium oxygen and carbon isotopic data from lacustrine carbonates formed in the southwestern uinta basin utah between the late cretaceous and late middle eocene reveal a two stage expansion in the drainage basin of lake uinta beginning at 53 ma culminating in the mahogany highstand at 48 6 ma a marked increase in 87 sr 86 sr ratios of samples from the main body of the green river formation is interpreted as the result of water overflowing the greater green river basin in wyoming and entering lake uinta from the east via the piceance creek basin of northwestern colorado this large new source of water caused a rapid expansion of lake uinta and was accompanied by a significant and rapid increase in the o isotope record of carbonate samples by 6 the periodic overspilling of lake gosiute probably became continuous at 49 ma when the lake captured low 18 o water from the challis and absaroka volcanic fields to the north however evaporation in the greater green river and piceance creek basins meant that the waters entering lake uinta were still enriched in 18 o by 46 ma inflows from the greater green river basin ceased resulting in a lowstand of lake uinta and the deposition of bedded evaporites in the saline facies of the green river formation we thus show that basin development and lake hydrology in the laramide foreland were characterized by large scale changes in cordilleran drainage patterns capable of confounding paleoaltimetry studies premised on too few isotopic systems samples or localities in the case of the north american cordillera of the paleogene we further demonstrate the likelihood that 1 topographic evolution of distal source areas strongly influenced the isotopic records of intraforeland basins and 2 a pattern of drainage integration between the hinterland and foreland may correlate in space and time with the southward sweep of hinterland magmatism

application of the change of sterane isomer ratios to the reconstruction of geothermal histories implications of the results of hydrous pyrolysis experiments abstract kinetic data for the change of the c 20 isomer ratio of 5 h 14 h 17 h steranes have been derived from a series of hydrous pyrolysis experiments on samples of the lower toarcian posidonia shale from northern germany the results are compared with other published kinetic data for the same apparent biological marker reaction it is shown that the sensitivity of these different sets of kinetic data varies drastically in the application to model calculations using predefined geothermal conditions the difference in sensitivity is hard to estimate from an inspection of the numerical values of activation energy and frequency factor alone a procedure for the selection of analytical sterane isomer ratios for kinetic assessment using a tti approach is demonstrated error calculations show what level of accuracy can be reached in the prediction of formation temperatures and burial depths when the kinetic data are applied to the reconstruction of geothermal histories of sedimentary basins

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

tertiary oils from upper assam basin india a geochemical study using terrigenous biomarkers abstract the upper assam basin in northeast india is a tertiary sub basin of the assam arakan basin hydrocarbons are present in the langpar formation upper palaeocene lakadong member of the sylhet formation lower eocene and the barail oligocene tipam lower miocene and girujan middle miocene formations in the basin a detailed study to understand the nature and origin of the oils from different stratigraphic horizons using terrigenous and other biomarkers has been carried out further the variation in maturities of oils occurring in different stratigraphic horizons has also been studied the study shows that rearranged oleananes oleananes and bicadinanes are present in these oils implying land plant input to their source rocks the oils have been classified into different groups using ratios of rearranged oleananes oleananes bicadinanes and steranes indicating presence of multiple source rocks in the basin with subtle variation in characteristics maturity studies show that oils from younger horizons barail tipam and girujan are more mature than oils from older horizons langpar and lakadong there is an apparent mismatch in maturity of oils as measured by different biomarker maturity parameters this is due to the mixing of two different charges of oils having different maturities and generated from two different source rock kitchens in the same reservoir principal component analysis pca of biomarker data has also been able to classify the oils into various groups a new parameter has been developed using ratios of rearranged oleananes for determining maturity of these oils

isotopic composition of uranium and thorium in crystalline rocks the 238u 234u 230th 232th system has been investigated in 84 silicic crystalline rocks obtained from drill cores surface and near surface samples in california wyoming colorado and illinois results of these analyses displayed on ternary diagrams with apexes for 238u 234u and 230th indicate five predominant geochemical processes that affected uranium in the rock 1 bulk uranium leaching where 238u and 234u were removed with little or no fractionation 2 preferential 234u leaching by alpha recoil displacement 234u recoil loss with lesser 238u loss 3 234u recoil loss with little or no 238u loss 4 uranium assimilation where both 238u and 234u were added with present day 234u 238u activity ratios varying from 0 8 to 1 2 and 5 addition of 234u and 230th by daughter emplacement processes 234u 230th recoil gain evidence for the existence of 234u and 230th recoil gain in rocks is the most important finding of this investigation radioactive disequilibrium occurs in the majority of rocks analyzed where 234u recoil loss is the predominant process associated with incipient weathering u assimilation and 234u 230th recoil gain occur under conditions of substantial water penetration along fractures and into weathered zones in the rocks relatively unfractured and petrographically fresh rocks from the uph 3 drill hole in northern illinois are closest to being in radioactive equilibrium for any suite of rocks included in this study and they demonstrate that equilibrium during the last 0 5 m y can be maintained over a substantial vertical distance where there has been little or no movement of water in the basement rock the 238u 234u 230th system can be a sensitive indicator of geologically recent u mobility and rock water interaction both in petrographically fresh core samples and in sealed fracture zones

biomarker and n alkane isotope profiles for tertiary oils relationship to source rock depositional setting abstract biomarker and n alkane isotope profiles have been measured for 29 late cretaceous tertiary oils from se asia china papua new guinea new zealand and the u s a the results are interpreted with respect to six kinds of source rock depositional setting fluvio deltaic fd freshwater transitional tr lacustrine lac saline lacustrine sal marine deltaic md and marine carbonate mc a comparison of biomarker and n alkane isotope results suggests that parameters such as the oleanane hopane ratio may overestimate the higher plant contribution to marine oils the abundance of bicadinanes is much more variable than that of oleanane probably because of a specific association with the highly resinous dipterocarp hardwoods of se asia however traces do occur in an oil from outside the paleogeographic range of the dipterocarp family confirming that there is also a more general angiosperm source the bicadinane isomeric distribution is shown to depend on maturity leading to new maturity parameters which are resistant to even very heavy biodegradation retention indices based on the regular hopane series are provided for the main bicadinane and methyl bicadinane isomers and for a group of oleanane related triterpanes of unknown structure the presence of the latter compounds may indicate locally deposited as opposed to transported higher plant matter in the source source rock depositional setting is the primary control on the shape of the n alkane isotope profile with negatively sloping curves being characteristic of fd and tr oils and flat or positively sloping curves typical of marine oils the difference is probably related to the bacterial reworking of higher plant matter in the fd environment a slight isotopic anomaly at n c 17 correlates with the abundance of algal derived steranes and may indicate a minor marine contribution to the source of an fd oil

petroleum generation and migration from talang akar coals and shales offshore n w java indonesia abstract the oligocene talang akar formation is the major source for petroleum oil and gas in the ardjuna sub basin source rock quality varies within the deltaic to marginal marine complex with coals deposited on the lower delta plain being distinctly oil prone whereas the surrounding delta plain shales are largely gas prone shales and drifted coals laid down in marine influenced interdistributary bay environments show increasingly oil prone characteristics possibly due to preferential transport of hydrogen rich plant components to more distal setting molecular characteristics of the coals and shales are similar with higher plant angiosperm biomarkers and their aromatic derivatives occuring widely kinetic studies of hydrocarbon generation and stimulated maturation experiments using hydrous pyrolysis indicate that the delta plain coals are the major source for crude oils in the basin with a secondary but minor contribution from marine influenced interdistributary bay shales delta plain shales are interpreted to expel gaseous products only the stratigraphic and spatial location of oil and gas fields were examined with respect to their position relative to oil and gas generating source rocks the field distribution could not be explained in terms of source rock geochemistry alone and phase behavior of petroleum during secondary migration was shown to exert an important influence on the distribution of oil and gas deposits in the basin

composition and origin of fuel from the hut of explorer robert falcon scott cape evans antarctica geochemical analyses of the fuel used for the motor driven sledges used by the explorer robert falcon scott for his 1911 1912 quest to the south pole indicate that it is a straight run gasoline the presence of bicadinanes oleanane and other oleanoid angiosperm markers indicate that the feedstock oil was likely to have been sourced from terrestrial source rocks of tertiary age in the south east asian region the overall chemical composition of the fuel in its present state indicates that it may have been too heavy for usage in polar regions

microbiotas from the late proterozoic chuar group northern arizona and uinta mountain group utah and their chronostratigraphic implications abstract samples of shales from the dominantly clastic upper proterozoic chuar and uinta mountain groups in northern arizona and utah yielded relatively abundant assemblages of acritarchs these are taxonomically varied and are interpreted as consisting of openwater cosmopolitan eukaryotic plankton the assemblages are compared with late proterozoic late riphean and early vendian c 800 700 ma sequences in the southern urals of the ussr the russian platform northern and southern scandinavia svalbard and east and north west greenland in all instances both the assemblages and discrete form taxa predate the varangerian vendian glacial event of the north atlantic region and this is taken to indicate a comparable age for glaciogenic rock units in western north america one new acritarch species vandalosphaeridium walcottii is erected and the partly megascopic species chuaria circularis is emended

rare earth elements in oligo miocenic pelitic sediments from lagonegro basin southern apennines italy implications for provenance and source area weathering the lagonegro units are a part of the southern apennines orogenic wedge the age of the lagonegro successions ranges from lower middle triassic to oligo miocene during late cretaceous and oligocene the deposition of calcareous clastic sediments occurred interbedded with shales flysch rosso fm during oligocene and early miocene in the mediterranean area an important variation of the tectonic regime occurred and siliciclastic sediments of the numidian basin unconformably lay on the meso cenozoic units of the lagonegro basin in the lucanian apennine the aquitanian langhian numidian flysch fm overlies the flysch rosso fm the shales of the flysch rosso fm have a peculiar geochemical fingerprint relative to typical shales of post archean age the abundance of ni and cr is significantly higher and the hree chondrite normalized patterns are steep with a gd yb ch 2 a supply of material from the african archean terranes could be the cause the palaeo weathering indices record changes at the source reflecting variations in the tectonic regime the oldest samples are derived from an environment in which steady state weathering conditions prevailed whereas the youngest samples are related to non steady state weathering conditions this difference could record deformational events that affected the mediterranean area during the oligocene and early miocene the sample at the top of the studied log has very high silica content and an abundant coarse grain sized fraction this suggests that this sample belongs to the numidian flysch fm the geochemical proxies of this sample are different from those associated with samples from the flysch rosso fm indicating that the source area of the numidian flysch fm did not include the archean terranes

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

quantifying the contribution of dust to alpine soils in the periglacial zone of the uinta mountains utah usa abstract profiles of alpine soils in the uinta mountains utah usa were investigated to determine how long term dust deposition has influenced soil properties in this environment field studies were focused on four above treeline sites all of which were apparently beyond the reach of erosive glacial ice during the pleistocene modern dust soil a and b horizons and local bedrock were compared in terms of major and trace element geochemistry along with sr and nd isotope compositions in all cases soil samples are a mixture of dust and local bedrock end members with a horizons more closely resembling dust and b horizons more similar to bedrock calculations estimate that these soil profiles contain 50 to 80 dust which is effectively mixed downward into the solum by cryoturbation because these landscape positions were not glaciated the total amount of dust contained within soil profiles is large relative to sites at lower elevation within the glacial limit in addition to altering physical properties of these soil profiles including horizonation and texture deposition of dust rich in base cations positively influences soil fertility

oleananes in oils and sediments evidence of marine influence during early diagenesis abstract the oleananes as markers for the angiosperms provide valuable source and age information when present in an oil nevertheless they are not quantitatively related to the land plant input and indeed their presence reflects only a small leak in diagenetic processes leading primarily to aromatic oleanoids because they are minor products the abundance of oleananes in terrigenous oils and sediments may be highly sensitive to changes in early diagenetic conditions here we present evidence that contact of plant matter with seawater during early diagenesis enhances the expression of oleananes in a mature sediment or oil oleananes are absent or present at very low concentrations in samples from the base of an eocene coal seam affected by postdepositional seawater intrusion however their abundance increases toward the top of the seam in correlation with organic sulphur dibenzothiophene phenanthrene and the homohopane index similarly in deltaic sediments from the south sumatra basin oleanane hopane is strongly correlated with indicators of marine influence such as c 27 c 29 steranes and the homohopane index in each case increasing oleanane abundance is accompanied by a reduction in the extent of aromatisation and for the south sumatra basin the proportion of a ring contracted oleananes an angiosperm derived miocene coal from the philippines deposited under freshwater conditions shows abundant aromatic oleanoids but no oleananes these results show that oleananes need to be used with caution as age and source markers in fluvio deltaic and lacustrine petroleum systems on the other hand their sensitivity to early diagenetic conditions may make them useful in locating effective source rocks in such systems

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

relationship of biomarker distribution to depositional environment phosphoria formation montana u s a from biomarker distributions it is possible to distinguish extracts from four different members facies meade peak rex retort and tosi of the permian phosphoria formation at little sheep creek montana these distributions relfect changes in floral and faunal distribution in response to a changing depositional environment and suggest that the retort and tosi members the second cycle of deposition were deposited under more anoxic conditions and at higher salinity than meade peak and rex members the first cycle correlations between biomarker indicators of anoxia and salinity suggest that anoxia was in part the result of a chemocline separating normal marine waters above from more saline bottom waters anoxia and salinity in the bottom waters increased with time making conditions in the basin progressively more hostile to benthic organisms development of extreme environmental conditions in continental shelf habitats such as those suggested by biomarker parameters at little sheep creek may have compounded spatial problems created by continental suturing suggested to be a cause of permian extinctions factor analysis indicates that four factors for 75 3 of the variance in biomarker ratios these factors are suggested to be source organisms types of eukaryotic plankton salinity eh and mineralogy the grandeur member of the phosphoria which is a typical reservoir rock for phosphoria derived oils yields an extract containing a novel c30 nitrogen containing steroid this unique steroid is not abundant in any other known extracts or oils which along with the extremely low porphyrin maturity parameter of all the extracts pmp 0 01 confirms the absence of migrated oils in the phosphoria at little sheep creek the biomarker ratios c29 ga a steranes ts ts tm triaromatic triaromatic monoaromatic steroids short long short chain monoaromatic steroids and short long short chain triaromatic steroids are commonly used to determine the thermal maturity of oils and source rock extracts however these ratios show considerable variation in core extracts of the same thermal maturity from different facies in contrast the thermal maturity parameters c29 20s 20s 20r steranes and porphyrin maturity parameter pmp show little variation indicating that these parameters are less affected by changes in depositional environment and may be most useful for thermal maturation determinations of phosphoria related oils and source rocks this study supports previous work suggesting environmental effects must be considered if correct determination of thermal maturity of an oil or extract is to be made this is especially true of oils and extracts from source rocks with high sulfur concentrations and or those deposited at elevated salinities

oceanic transport of fossil dammar resin the chemistry of coastal resinites from south australia abstract fragments of resin and fossilised resin resinites occasionally wash ashore along the southern australian coast chemical and isotopic analyses were carried out on a suite of coastal and reference resinites to determine the likelihood of a local as opposed to a distant origin all of the coastal resinites were found to contain a polymer based on the sesquiterpenoid cadinene skeleton and were markedly different to the diterpenoid resinites found in local victorian coals the coastal resinites closely resemble both fossil and recent dammar resin a material associated primarily with the tropical angiosperm hardwoods of southeast asia and one which has no known australian source minor variations in the composition of our resinite samples are attributed to differences in their thermal history these findings confirm the viability of long distance oceanic transport not only for the resinites but also for the waxy bitumens that strand along the same coastline analytical data on the coastal resinites also help to clarify the role of dammar resin in generating bicadinanes a class of source and age specific triterpanes found commonly in the cainozoic oils and sediments of southeast asia

trimethylnaphthalenes in crude oils and sediments effects of source and maturity abstract three sedimentary sequences and a number of crude oils have been analysed for trimethylnaphthalenes tmns using gas chromatography the sediments were found to contain enhanced relative abundances of 1 2 5 tmn and 1 2 7 tmn in samples of cretaceous age and younger this was especially pronounced in lower maturity sediments containing type iii organic matter older samples containing type iii organic matter were found to contain enhanced relative abundances of 1 2 5 tmn and lower relative abundances of 1 2 7 tmn 1 2 7 tmn appears to be derived directly from the structural degradation of oleanane type triterpenoids present in angiosperms and as such is proposed as a marker for this class of plant and indirectly therefore also for samples deposited since the early cretaceous the crude oils have been classified according to their trimethylnaphthalene compositions this classification enables crudes of higher plant origin to be identified and to be further classified according to whether the organic matter pre dated or post dated the evolution of angiosperms

composition and weathering conditions of paleoproterozoic upper crust of bundelkhand craton central india records from geochemistry of clastic sediments of 1 9ga gwalior group abstract the 1 9 ga gwalior group represents one of the major paleoproterozoic depositional basin of bundelkhand craton and is comprised of 1 km thick unmetamorphosed and undeformed sedimentary succession with basal clastic sequence of sandstone shale association par formation and an upper chemogenic bif rich sequence morar formation the geochemical examinations of the basal clastic rocks are the subject of present study the compositional maturity and extreme quartz enrichment in sandstones of gwalior group suggest slow upliftment and high in situ weathering of basement terrains in a stable platformal setting these clastic sediments are characterized by strong depletion of mobile constituents like ca sr and na high plagioclase index of alteration pia values and strong positive correlation between al 2 o 3 and tio 2 indicating severe weathering of upper crust positive correlation between feo t and tio 2 suggests fe retention in paleoweathering profiles and is attributed to oxygenated atmosphere post depositional potash metasomatism is indicated in a cn k systematics of these sediments and k enrichment from near zero to as high as 38 is inferred with most of the shale samples show 30 extraneous k 2 o additions depleted transition element ni cr co sc contents elevated large ion lithophile element lile k rb ba th light rare earth elements lree contents fractionated rare earth element ree patterns strong negative eu anomalies in these sediments point toward k rich intracrustal granitic source component steeper ree patterns avg la yb n 12 57 compared to basement granites and conspicuous depletion of y over other liles in auc normalized spidergram also suggest a heavy rare earth element hree depleted ttg source component minor contribution from tholeiitic mafic rock is evidenced from th sc sc la sc sc th systematics and positive correlation of transition elements with feo t and tio 2 mixing calculations on the ree data suggest that upper continental crust of bundelkhand craton was constituted of 40 granite 40 ttg and 20 mafic rocks this is in contrast with the present day composition of bundelkhand granite gneiss complex bggc that contains 90 high k granite the data suggest unroofing of granite batholiths by means of erosion and upliftment of supracrustal ttg cover

changes in hydrocarbon maturity indices with coal rank and type buller coalfield new zealand abstract the buller coalfield south island new zealand is an inverted late paleogene basin that contains middle eocene bituminous coals which exhibit considerable variation in both coal rank across basin and coal type in seam twenty two fractionated bitumen extracts of brunner coal measures coal samples from 12 drillholes were analyzed by gc and gc ms to characterize the effect of coal rank and type on conventional hydrocarbon maturity indices at the beginning and end of the oil window 0 56 1 26 ro max the carbon preference index pristane phytane and isoprenoid n alkane ratios evolve throughout the high volatile bituminous b rank stage while other biomarker ratios 18 h 22 29 30 trisnorneohopane 17 h 22 29 30 trisnorhopane ts tm 18 h 21 h 30 norneohopane c 29 ts 17 h 21 h 30 norhopane and c 30 diahopane hopane do not show appreciable change in value until medium volatile bituminous rank various aromatic based ratios appear to be more effective in delineating rank throughout the entire oil window in particular the methylphenanthrene index and vitrinite reflectance are positively correlated over the entire bituminous rank range however subtle changes in depositional conditions variable coal type complicate these rank estimates within a given coal seam variation in cpi isoprenoid n alkane and hopane sterane ratios appear to be related to the hydrogen content of the coal while the homohopane index and the oleanane hopane ratio covary with sulfur content as with depressed vitrinite reflectance values mpi is similarly lowered in the perhydrous samples the mechanisms that control these hydrocarbon parameters during deposition and diagenesis are complex and convoluted however changes in bacterial activity and community with marine incursion appear to play an important role due to these anomalies none of the hydrocarbon maturity indices calculated can be singularly used to constrain coal rank

tectonic setting and provenance of the neoproterozoic uinta mountain and big cottonwood groups northern utah constraints from geochemistry nd isotopes and detrital modes abstract the neoproterozoic uinta mountain group was deposited in an east trending intracratonic rift bounded on the north by an active fault system and opening into a shallow sea on the west where the big cottonwood group was deposited in an estuary although this rift may have been associated with the early stages in the breakup of rodinia it was not an aulacogen geochemical nd isotope and detrital mode studies indicate that uinta mountain group sediments were derived from mixed archean and paleoproterozoic sources with the former dominating big cottonwood group sediments appear to have been derived predominantly from paleoproterozoic sources the archean sediment source is the wyoming craton and source rocks comprised dominantly granites enriched in th u y zr hf and ree the relative abundance of enriched granite implied by sedimentary rocks of the uinta mountain group indicates that the wyoming craton is anomalous compared to other archean cratons cia values and a cn k relationships in shales of the uinta mountain and big cottonwood groups indicate high degrees of weathering of sources probably in subtropical to tropical climates supporting a near equatorial location for southwestern laurentia at about 800 ma differences in the nd isotopic composition between the big cottonwood group and neoproterozoic sedimentary rocks in western utah and northeast nevada suggest a northwest striking uplift in northwest utah possibly ancestral to the paleozoic toole uinta arch

geochemical characterization and source investigation of oils discovered in khoraghat nambar structures of the assam arakan basin india abstract we examined the geochemical compositions of the newly discovered bokabil and sylhet oils and of the extracts of potential source rock samples from the khoraghat nambar area of the assam arakan basin india stable carbon isotopic compositions and a number of biomarkers indicate that oils in the bokabil formation early to middle miocene can be correlated across the khoraghat and nambar fields however oil from the sylhet formation middle to late eocene is distinct from those in the bokabil formation late eocene to early oligocene barail coal shale and middle to late eocene kopili shale sequences are identified as potential source rocks both strata contain organic matter predominantly derived from higher land plants however different organofacies exist for barail coal shale and kopili shale sequences that can be distinguished by the stable carbon isotopic compositions and biomarker distributions an oil source correlation study shows that barail rock extracts are genetically correlatable with the bokabil oils whereas kopili rock extracts have similar source specific parameters to those of the sylhet oil thus the study suggests the presence of two petroleum systems in the khoraghat nambar area the barail bokabil and the kopili sylhet petroleum systems barail and kopili sediments from the study area are of lower maturity than the oils suggesting that the actual source strata are more mature equivalents likely to be present in the naga schuppen zone therefore areas in and around the naga schuppen zone where better reservoir facies are expected are favoured targets for further exploration

constraints upon the use of 24 ethylcholestane diastereomer ratios as indicators of the maturity of petroleum abstract we have measured the ratio 20 s 20 s 20 r the relative abundances of the 24 ethylcholestane diastereomers in nine pairs of closely adjacent samples of coals and shales which represent a range of geological ages and different sedimentary basins within some sample pairs the values were similar in others they were very different the differences between the values for coal and shale members of pairs are attributed to effects of sediment matrix type upon the processes which cause the changes in the ratio the kinetic parameters e and s for the changes in the 20 s 20 s 20 r ratio have been estimated using previously published measurements for the hod 1 well shale and jupiter 1 well coal and these values were found to be very different the process in the coal sequence has a much lower activation energy and is therefore less responsive to differences in heating rate regimes than is the case for the shale sequence values of the 20 s 20 s 20 r ratio in two other sequences are shown to be consistent with this explanation and the implications of these observations for the practice of using sterane isomer ratios for assessment of maturity of sediments and crude oils are discussed

higher plant biomarker signatures of early eocene sediments of north eastern india abstract the biomarkers molecular fossils of paleobiota have been studied in detail from a coal bearing sequence of early eocene lakadong sandstone member of sylhet formation of upper assam basin ne india using gas chromatography mass spectrometry corresponding hydrocarbon source potential of the same unit has been studied using rock eval pyrolysis the rock eval data suggest dominant terrestrial land plant contribution i e type iii kerogen and the sediments of the section had entered the early stage of catagenesis the alkane and isoprenoid distributions are characterized by odd over even preference oep 1 1 1 2 of n alkanes and high pristane phytane ratio 2 9 7 6 which corroborate the rock eval data the distribution of aliphatic biomarkers is characterized by dominance of c24 tetracyclics over c23 tricyclics high concentration of des e hopane moderate to high c29 c30 hopane ratio extremely low oleanane index and low c35 homohopane index the extremely low oleanane index is correlated with a high degree of aromatization of oleanane skeleton favoured by acidic swampy depositional environment the presence of diterpanes at the base of the early eocene section indicates contribution from gymnosperms coniferales order of land plants whereas angiospermous biomarkers with oleanoid skeleton are also preserved this pattern subsequently evolved to angiosperm dominated towards the top of the section with no gymnosperm signature indicating possible climatic variation during the early eocene towards the top of the section presence of bicadinanes indicates contribution of dipterocarpaceae family of trees and advent of the evergreen tropical rain forest element in eastern india in early eocene similar to the pattern found in western india e g cambay and kutch basins

cadalenes and norcadalenes in organic rich shales of the permian irati formation parana basin brazil tracers for terrestrial input or also indicators of temperature controlled organic inorganic interactions abstract cadalene isocadalene and a series of norcadalenes were identified in black shales of the permian irati formation in the northeastern and central eastern parana basin brazil the origin of their isomers with an isopropyl substituent is potentially related to higher plants and likely reflects the spreading of pteridophytes and gymnosperms after the glaciation of southern gondwana a general increase in the relative abundance of isocadalene 1 6 dimethyl 3 isopropylnaphthalene the isomer co occurs in with increasing thermal maturity at the base of the amaral machado quarry northeastern basin and refers to the acid catalyzed rearrangement of cadalene 1 6 dimethyl 4 isopropylnaphthalene the isomer due to the presence of montmorillonite via an organic inorganic interaction this localized and incipient maturation can be related to diabase sills of the serra geral formation similar maturation due to heating also affected the distribution of the norcadalenes by thermally stabilizing their isomers with an isopropyl substituent in addition to the formation of related compounds with an ethyl substituent based on this a norcadalene ratio is proposed which is the sum of the 1 6 dimethyl 4 ethylnaphthalene and 1 6 dimethyl 3 ethylnaphthalene over the sum of the 1 isopropyl 4 methylnaphthalene and 1 isopropyl 7 methylnaphthalene the results of this ratio and the established cadalene ratio resemble each other whereas samples from the sao mateus do sul quarry central eastern basin were not affected by thermal maturation and are characterized by a uniform distribution of the cadalenes and norcadalenes

sources of middle proterozoic to early cambrian siliciclastic sedimentary rocks in the great basin a nd isotope study the nd isotopic compositions of middle proterozoic to early cambrian terrigenous sedimentary rocks in the great basin united states were determined to identify the source areas of the siliciclastic detritus and to constrain models for the early tectonic evolution of the western margin of the continental united states in the southwestern great basin and vicinity nd isotope data from the intracratonic middle to late proterozoic pahrump group reveal that the coarse grained detritus from the crystal springs and the younger kingston peak formations including apparent glacial dropstones was derived from the local proterozoic basement province 1 as defined by nd isotope data fine grained detritus derived from other proterozoic crustal terranes provinces 2 or 3 was identified in the southernmost exposed portions of the pahrump group and corresponds to more distally derived material originally eroded from proterozoic basement farther to the south and east coarse and fine grained sedimentary material composing the overlying early cambrian miogeoclinal strata were also derived primarily from local province 1 basement rocks but the occurrence of detritus derived from province 2 or 3 crust is widespread geographically the deposition of sediment derived from province 2 or 3 across the developing continental shelf presumably reflects thermal subsidence and progressive marine encroachment of the ancient continental margin within the middle proterozoic to early cambrian section only the arkosic middle member of the wood canyon formation and the correlative deeper marine andrews member of the campito formation have measured nd values greater than 15 6 to 4 these units were apparently derived from a local 1 b y old granitic source exposed during the early cambrian period to the northeast of present day southern nevada the tectonic settings of the formation and subsequent uplift of this granitic terrane are unknown but erosion of the granite generated excellent nd isotopic marker beds that should prove useful in correlating early cambrian miogeoclinal sedimentary rocks throughout southwestern north america in the north central great basin late proterozoic miogeoclinal sedimentary rocks of the trout creek and mccoy creek groups show a marked shift from province 2 or 3 to province 1 sources through time this shift is consistent with a change in topography related to the emergence of the tooele uinta arch as an area of positive relief the nd data provide the first evidence that this structure was present in this region as early as latest proterozoic time as in the southern great basin however the isotope data indicate that sediments deposited in the late proterozoic era in the northern regions were dominantly derived from sources in the local precambrian basement

composition and provenance of the macigno formation late oligocene early miocene in the trasimeno lake area northern apennines abstract sandstone petrography and mudstone mineralogy and geochemistry of the late oligocene early miocene terrigenous deposits of the macigno fm of the trasimeno lake area central italy provide new information on provenance paleoenvironment palaeoclimate and geodynamics during the early stages of the northern apennines foreland basin setting sandstones are rich in trace fossils and are quartzofeldspatic with various crystalline phaneritic mostly granitoids and medium low grade metamorphic rock fragments volcanic and sedimentary lithic fragments are rare the mudstone mineralogy contains a large amount of phyllosilicates quartz and feldspars and small amount of calcite which increases in the mid part of succession palaeoweathering indices chemical index of alteration with and without cao value cia and cia respectively suggest a source area that experienced low to moderate weathering and low recycling processes on average cia 66 4 and cia 69 7 furthermore very low and homogeneous values of rb k ratios the sandstone and mudstone composition reflects a provenance derived from uplifted crystalline rocks the different amount in feldspars the variety of lithic fragments the occurrence of mafic and carbonate input coupled with evidence of multi directional flows suggest a provenance from different source areas the geochemical proxies indicate a provenance from both felsic and mafic sources predominantly for the maesta section that shows cr v values ranging from 1 15 to 3 36 typical of source areas composed of both felsic and mafic rocks the western central alps are inferred to be the main source area of the macigno foreland system but significant signals from the mesomediterranean microplate are also testified these new data suggest that the macigno fm was probably located in a peculiar area which received either distal fine turbidite flows from the northernmost alpine area and residual sandy debris flows coming from the westernmost alps

high resolution δ13c stratigraphy of the chuar group ca 770 742 ma grand canyon implications for mid neoproterozoic climate change a high resolution c isotope record based on 13 c org from organic rich shales and 13 c carb from dolomites in the ca 770 742 ma chuar group provides important new data for evaluating the signifi cance of large magnitude c isotope anomalies in neoproterozoic climate change three successive large magnitude isotopic excursions 8 15 are interpreted to represent primary seawater values based on a series of diagenetic tests and they are not associated with evidence of signifi cant long term 10 6 10 7 m y sea level change nor glaciomarine deposits intrabasinal correlation of 13 c org values suggests that most chuar shales record primary values and is consistent with previously reported h c ratios of 0 49 indicating that chuar shales experienced minimal thermal alteration although some chuar dolomites reveal early diagenetic alteration their 13 c dol values typically fall near those of coeval least altered dolomites or organic rich shales relative to dolomite values the chuar carbon record is interpreted to refl ect predominantly primary organic carbon 13 c values and contains suf

resetting of neodymium isotopes and redistribution of rees during sedimentary processes the early proterozoic chelmsford formation sudbury basin ontario canada abstract the rees abundances and neodymium isotope compositions of sandstones and siltstones from the early proterozoic chelmsford formation reveal that the rees in some samples were redistributed during the early proterozoic by surficial processes and that prior to redistribution the nd isotope system was partially reset the chelmsford formation is a coarse grained turbidite sequence the youngest of three clastic units that fill the sudbury basin in ontario it is constrained to have been derived from nearby late archean superior province rocks by petrography major and trace element chemistry and pb isotopic compositions of whole rocks and feldspar although ree patterns and nd model ages for samples from around the base of the formation reflect their derivation from undisturbed superior province rocks tdm 2800 ma five samples from higher in the stratigraphic section show evidence that up to 60 of their la has been removed and sm nd has increased by up to 60 these samples also have anomalously high nd model ages tdm 3400 to 4400 ma the presence of pronounced positive ce anomalies in the samples with anomalous tdm indicates the influence of surficial processes on the ree composition the data scatter about a vertical array on a plot of f sm nd vs ndt 1800 nd calculated at 1800 ma approximately the depositional age with values of f sm nd between 0 45 and 0 14 mixing of nd from other sources is difficult to reconcile with the petrography major and trace element geochemistry and nd and pb isotopes removal of an lree enriched phase from the sedimentary system provides a viable mechanism to produce the ree and nd isotopic characteristics of the chelmsford formation samples neodymium isotopes require that this phase was partially isotopically equilibrated with the matrix sediment near the time of sedimentation this study shows the dangers of indiscriminate use of nd model ages in provenance studies and demonstrates that the simultaneous examination of sm nd and nd isotopes on f sm nd vs nd or isochron plots is required for the recognition of sedimentary redistribution of the ree

palaeomagnetism of the teschenitic rocks lower cretaceous in the outer western carpathians of poland constraints for tectonic rotations in the silesian unit summary results of palaeomagnetic investigations of the lower cretaceous teschenitic rocks in the silesian unit of the outer western carpathians in poland bring evidence for pre folding magnetization of these rocks the mixed polarity component reveals inclinations between 56 and 69 which might be either of cretaceous or tertiary age apparently positive results of fold and contact tests in some localities and presence of pyrhotite in the contact aureole suggest that magnetization is primary although a neogene or earlier remagnetization cannot be totally excluded since inclination only test between localities gives syn folding results higher palaeoinclinations 66 69 correlate with a younger variety of teschenitic rocks dated for 122 120 ma while lower inclinations 56 60 with an older variety 138 133 ma this would support relatively high palaeolatitudes for the southern margin of the eurasian plate in the late part of the early cretaceous and relatively quick northward drift of the plate in this epoch together with the silesian basin at its southern margin declinations are similar to the cretaceous tertiary palaeodeclinations of stable europe in the eastern part of the studied area but rotated ca 14 70 counter clockwise in the western part this indicates together with older results from czech and slovakian sectors of the silesian unit a change in the rotation pattern from counter clockwise to clockwise at the meridian of 19 e the rotations took place before the final collision of the outer carpathians nappe stack with the european foreland