evidence for mixed and biodegraded crude oils in the socororo field eastern venezuela basin this work presents a geochemical study of crude oils from the socororo field socororo major area in the maturin sub basin of the eastern venezuelan basin the v ni total concentrations and v v ni ratios suggest the presence of two oil groups these oils are heavy aromatic asphaltic and according to their sulfur content api gravity and hydrocarbon compositions fall into the same two groups established from the v and ni proxies although the analyzed crude oils show evidence of biodegradation it was possible to determine based on various biomarkers parameters that the oils originated from marine organic matter in a marine carbonate or marine marl source rock deposited under anoxic to suboxic conditions the oils were generated near the peak of the oil window distributions of n alkanes isoprenoids hopanes and steranes combined with a prominent unresolved complex mixture ucm indicate that the oils are biodegraded moreover the presence of pristane and phytane along with alteration of hopanes and steranes and the presence of 25 norhopanes reveals that these oils are mixtures showing different levels of biodegradation sulfur content v and ni concentration and saturate aromatic resin and asphaltene sara composition provide additional evidence for oil mixing such mixed oils originate from several episodes of charging and biodegradation in the reservoirs the first charge was severely biodegraded and many biomarkers susceptible to degradation n alkanes acyclic isoprenoids terpanes methyl hopanes methyl steranes and steranes were extensively altered or completely removed the second oil charge was subjected to a lower degree of biodegradation and only the n alkanes show significant biodegradation both oil charges seem to come from the same source rock which was deposited under variable redox conditions moreover due to their similar maturity the generation and migration of these oils to reservoirs likely occurred close together in time

a geochemical reconstruction of oil generation in the barrow sub basin of western australia abstract a suite of crude oils and petroleum source rock extracts from the barrow sub basin of western australia have been analysed for biological marker compounds by capillary gc ms and for volatile hydrocarbons by whole oil capillary gc these analyses were used to calculate values for twenty three biomarker parameters in order to assess aspects of source type maturity migration and biodegradation of the hydrocarbons the crude oils had a source in the upper jurassic dingo claystone formation these hydrocarbons accumulated in the reservoir sands and in some cases were biodegraded several accumulation and biodegradation episodes have been recognised while the basin continued to subside which resulted in a suite of oils showing marked differences in composition

the origin of separate oil and gas accumulations in adjacent anticlines in central iran abstract in central iran two adjacent anticlines contain hydrocarbons within the late oligocene early miocene qom formation the anticlines formed at approximately similar times late miocene pliocene have similar overall geometries but the alborz anticline is an oil field while the sarajeh anticline is a gas field and both are underfilled structures basin modeling and structural restorations identified why the two different accumulations developed the sarajeh and alborz anticlines are modified detachment anticlines asymmetric development of growth strata on the sw margin of the folds was caused by salt withdrawal and normal fault activity on the basin margin which modified the detachment fold style and tilted the basal detachment to the sw the detachment dies out to the ne as the basal lower red formation evaporites pinch out in the same direction yet the alborz anticline is north vergent while the sarajeh anticline is south vergent the mini salt withdrawal basin is best developed on the southern limb of the sarajeh anticline and is responsible for the sw vergence this difference in vergence permitted the alborz anticline to attain 4 way dip closure earlier in its structural history than the sarajeh anticline and consequently the trap was at least partially developed as a four way closure during oil generation and expulsion for the sarajeh anticline oil migrated across the fold when it was still unclosed continued subsidence of the sw fold limb resulted in gas generation and expulsion during the time when the fold attained closure

syn depositional alteration of coral reef framework through bioerosion encrustation and cementation taphonomic signatures of reef accretion and reef depositional events the development of coral reef framework and the preservational character of both in situ and rubble coral is strongly influenced by a range of physical chemical and biologically mediated taphonomic processes these operate at or just below the reef framework water interface and can be defined as having either a constructive or destructive effect upon primary reef framework i e coral constituents constructional activities add additional calcium carbonate to the primary framework structure via secondary framework growth and early cementation destructive processes which remove or degrade primary and secondary framework carbonate are associated with the effects of either physical mainly storm disturbance or biological erosion termed bioerosion key bioeroding groups include the grazing fish and echinoid groups as well as the activities of an array of infaunal borers these include specific groups of sponges bivalves and worms termed macroborers as well as cyanobacteria chlorophytes rhodophytes and fungi termed microborers the relative importance of each process and the rates at which they operate vary spatially across individual reef systems in addition many of these processes leave distinctive signatures on or in the coral framework in some cases e g calcareous encrusters these are the skeletons of the organisms themselves whilst in other cases the organism may leave behind a trace of their activity e g macro and microborers these represent useful palaeoenvironmental tools firstly because they often have good preservation potential and secondly because the range and extent of many of the individual species groups and processes involved exhibit reasonably well constrained environment and or depth related distributions as a result these taphonomically important organisms or processes can be used to delineate between reef environments in core or outcrop and to aid the interpretation of reef depositional processes and events this review summarises current understanding regarding the distribution of these species processes within contemporary reef settings and considers the suites of taphonomic signatures that may aid in the recognition and interpretation of depositional environments and events

facies analysis and palaeoenvironmental interpretation of the late oligocene attard member lower coralline limestone formation malta the oligocene represents a key interval during which coralline algae became dominant on carbonate ramps and luxuriant coral reefs emerged on a global scale so far few studies have considered the impact that these early reefs had on ramp development consequently this study aimed at presenting a high resolution analysis of the attard member of the lower coralline limestone formation late oligocene malta in order to decipher the internal and external factors controlling the architecture of a typical late oligocene platform excellent exposures of the lower coralline limestone formation occurring along continuous outcrops adjacent to the victoria lines fault reveal in detail the three dimensional distribution of the reef associated facies a total of four sedimentary facies have been recognized and are grouped into two depositional environments that correspond to the inner and middle carbonate ramp the inner ramp was characterized by a very high energy shallow water setting influenced by tide and wave processes this setting passed downslope into an inner ramp depositional environment which was colonized by seagrass and interfingered with adjacent areas containing scattered corals the middle ramp lithofacies were deposited in the oligophotic zone the sediments being generated from combined in situ production and sediments swept from the shallower inner ramp by currents compositional characteristics and facies distributions of the attard ramp are more similar to the miocene ramps than to those of the eocene an important factor controlling this similarity may be the expansion of the seagrass colonization within the euphotic zone this expansion may have commenced in the late oligocene and was associated with a concomitant reduction in the aerial extent of the larger benthonic foraminifera facies stacking pattern analysis shows that the depositional units parasequences at the study section are arranged into transgressive regressive facies cycles this cyclicity is superimposed on the overall regressive phase recorded by the attard succession furthermore a minor highstand correlated with the ru4 ch1 sequence and subsequent minor lowstand ch2 sequence have been recognized the biota assemblages of the attard member suggest that carbonate sedimentation took place in subtropical waters and oligotrophic to slightly mesotrophic conditions the apparent low capacity of corals to form wave resistant reef structures is considered to have been a significant factor affecting substrate stability at this time the resulting lack of resistant mid ramp reef frameworks left this zone exposed to wave and storm activity thereby encouraging the widespread development of coralline algal associations dominated by rhodoliths

short term biomarker variability in the monterey formation santa maria basin abstract forty eight samples of a 370 ft miocene monterey formation core from the union leroy 51 18 well santa maria basin california are examined for source rock potential and molecular distributions total organic carbon content rock eval pyrolytic yield vitrinite reflectance and distribution of regular steranes tricyclic and pentacyclic terpanes and aromatic steroids are measured the present day temperature range through the sampled interval is estimated to be less than 5 c maturity differences among samples are negligible source rock potential and molecular distribution differences are considered to arise entirely from the effects of source input diagenesis including lithologic effects and migration the sampled section is comprised of siliceous and phosphatic carbonate lithofacies and covariances between geochemical parameters source potential and biomarker distribution and lithofacies are recognized several molecular parameters change systematically with depth lithology including ethylcholestane ratios and c 20 and c 22 sterane and hopane epimer ratios the siliceous lithofacies possesses higher moretane hopane tricyclic pentacyclic terpane and sterane terpane ratios and lower mono mono tri aromatic steroid ratios bisnorhopane hopane ratios are up to 40 times higher in the phosphatic carbonate lithofacies than in the siliceous lithofacies increased relative concentrations of aromatic steroids are attributed to sulfur sterol reactions during very early diagenesis whereas increased relative bisnorhopane amounts are considered to result from massive input of specific anaerobic biota although kerogen elemental ratios change abruptly at the lithofacies boundary molecular distributions within the extractable organic matter change gradually beginning about 30 ft 9m above this interface this gradual change is tentatively attributed to upward migration of hydrocarbons originating in the phosphatic carbonate lithofacies probably through fractures within the lower part of the siliceous lithofacies interval

arabia eurasia continental collision insights from late tertiary foreland basin evolution in the alborz mountains northern iran a poorly understood lag time of 15 20 m y exists between the initial arabia eurasia continental collision in late eocene to early oligocene time and the acceleration of tectonic and sedimentary processes across the collision zone in the early to late miocene the late eocene to miocene pliocene clastic and shallow marine sedimentary rocks of the kond eyvanekey and semnan basins in the alborz mountains northern iran offer the possibility to track the evolution of this orogen in the framework of collision processes a transition from volcaniclastic submarine deposits to shallow marine evaporites and terrestrial sediments occurred shortly after 36 ma in association with reversals in sediment provenance strata tilting and erosional unroofing these events followed the termination of subduction arc magmatism and marked a changeover from an extensional to a contractional regime in response to initiation of continental collision with the subduction of stretched arabian lithosphere this early stage of collision produced topographic relief associated with shallow foreland basins suggesting that shortening and tectonic loading occurred at low rates starting from the early miocene 17 5 ma flexural subsidence in response to foreland basin initiation occurred fast sediment accumulation rates and erosional unroofing trends point to acceleration of shortening by the early miocene we suggest that the lag time between the initiation of continental collision 36 ma and the acceleration of regional deformation 20 17 5 ma reflects a two stage collision process involving the soft collision of stretched lithosphere at first and hard collision following the arrival of unstretched arabian continental lithosphere in the subduction zone

cretaceous and paleogene saline lacustrine source rocks discovered in the southern junggar basin nw china abstract saline lacustrine source rocks in china provide the resource basis for many giant oil fields here we report the first discovery of such source rocks in the piedmont area of the northern tianshan mountains in the southern junggar basin of nw china these source rocks are cretaceous and paleogene in age organic geochemistry and trace element data suggest that these mudstones were formed in a brackish saline lacustrine environment characterized by deep water and reducing conditions and in a warm and dry paleoclimate evidence for this environment includes mudstone pr ph values of 0 4 and negative ce and eu anomalies the total organic carbon toc contents of these cretaceous and paleogene mudstones are typically 0 5 with maximum values of 1 45 and 2 22 respectively signifying moderate to high organic matter abundance rock eval and kerogen analyses suggest that the organic matter was dominated by type ii kerogen the mudstones are generally thermally mature suggesting favorable conditions for hydrocarbon particularly oil generation oil source correlation confirms the oil generation of these two sets of source rocks whose development are controlled mainly by reducing environments these cretaceous and paleogene mudstones should therefore be a target for regional exploration in the southern junggar basin in addition to the known gas producing jurassic rocks this oil bearing potential is unique amongst the early cretaceous and eocene oligocene central asian petroliferous basins as the eastern portion of this realm is considered to host predominantly jurassic coal based source rocks giving rise to numerous large gas fields rather than oil resources

origin and occurrence of 25 norhopanes a statistical study abstract the alkane fraction of more than 200 rocks biodegraded oils and non biodegraded oils have been analysed by means of computerized gc ms in order to investigate the effect of natural biodegradation on the occurrence of demethylated hopanes i e 17 25 norhopanes the results obtained indicate that 25 norhopanes are preexisting biomarkers the concentration of which is enhanced by selective biodegradation of more readily degradable homologs i e regular hopanes rather than by demethylation of hopanes in reservoirs however the use of 25 norhopane enrichment as a palaebiodegradation indicator in apparently non biodegraded oils is still valuable providing the initial background content in the corresponding source rocks is known furthermore 25 norhopanes appear to be diagnostic of specific environmental conditions marine and lacustrine source rocks dysoxic and not very hypersaline lastly one other novel bacterially resistant rearranged hopanoic compound namely a c29 neohopane is applicable for both biodegradation and maturation evaluation

late miocene deformation kinematics along the nw zagros fold thrust belt kurdistan region of iraq constraints from apatite u th he thermochronometry and balanced cross sections

timing of uplift in the zagros belt iranian plateau and accommodation of late cenozoic arabia eurasia convergence the motion of arabia was stable with respect to eurasia over the past 22 ma deformation and exhumation in the zagros is seen to initiate at the same time as argued by new detrital thermochronologic constraints and increasing accumulation rates in synorogenic sediments a recent magnetostratigraphic dating of the bakhtyari conglomerates in the northern fars region of the zagros further suggests that shortening and uplift in the zagros folded belt accelerated after 12 4 ma available temporal constraints from surrounding collision belts indicate that shortening and uplift focused in regions bordering the iranian plateau to the south between 15 and 5 ma as boundary velocity was kept constant this requires concomitant decreasing strain rates in the iranian plateau slab detachment has been proposed to explain the observed changes as well as mantle delamination but the insignificant change in the arabian slab motion and lack of unambiguous constraints make both hypotheses difficult to account for it is proposed based on a review of shortening estimates provided throughout the arabia eurasia collision that the total 440 km of convergence predicted by geodesy and plate reconstruction over the past 22 ma can be accounted for by distributed shortening i suggest that the topography and expansion of the iranian plateau over late miocene pliocene time can be reproduced by the progressive thickening of the originally thin iranian continental lithosphere presumably thermally weakened during the eocene extensional and magmatic event

the occurrence of 19 28 bisnorlanostane derivatives in a plant fossil a novel geochemical degradation process of triterpenoids abstract four novel triterpene ketones bearing 24 methyl 28 nor and 24 methyl 19 28 bisnor 5 lanostane skeletons were identified in a fossil of a stem of a plant belonging to the lauraceae family the structures of these compounds have been determined by comparison of their spectral data with those of authentic specimens derived from lanosterol and 24 methylenecycloartanol this is the first finding of compounds bearing a 19 28 bisnorlanostane skeleton which implies a novel possible microbiological pathway of degradation of lanostanes in the sedimentary environment

biomarker characterisation and hydrous pyrolysis of bitumens from tertiary volcanics queen charlotte islands british columbia canada abstract a number of bitumen samples have been recovered from vugs and fractures in outcropping tertiary basalts of the queen charlotte islands off the west coast of british columbia canada n alkanes and acyclic isoprenoids are not present and the polycyclic biomarker distribution of the four samples analyzed by gc and gc ms has been altered one sample contains no remaining recognizable biomarkers two bitumens were also obtained from lower jurassic potential source rocks including one from the sandilands formation which was considered previously to be the most likely source of the tertiary bitumens although these two bitumens were also taken from outcrops they are considerably less biodegraded the sandilands formation bitumen contains 28 30 bisnorhopanes and since these compounds were not detected in the tertiary bitumens there is no evidence from the initial results for a sandilands formation contribution to the hydrocarbons in the tertiary basalts the presence of 18 h oleanane in the saturate fraction of two of the tertiary bitumens from widely separated locations indicates that they are at least partially sourced from tertiary organic matter because the distribution of biomarkers in some samples has been severely affected by biodegradation the asphaltenes of the bitumens were hydrously pyrolysed and the saturate fractions of the resulting pyrolysates analysed for possible additional information on the origin of the bitumens the pyrolysates from the more degraded samples contain compounds not detected in the saturate fractions of the original bitumen and show some of the expected characteristics of the original non degraded bitumen however the compounds most useful for correlation are not present in the pyrolysates apparently due to their non incorporation into the kerogen macromolecule our results suggest that hydrous pyrolysis of asphaltenes is of limited use in the correlation of biodegraded samples and in determining their origins

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

evolution of a late jurassic carbonate evaporite platform conecuh embayment northeastern gulf coast u s a successive time slice lithofacies maps of the smackover haynesville depositional sequence constrained by marker beds an interpreted maximum flooding surface and interpreted sequence boundaries show an onlapping and retrograding sequence of lithologies characteristic of a transgressive systems tract tst the tst is followed by several prograding sequences characteristic of a highstand systems tract hst and stacked shelf margin wedges smw comparison of stratigraphic cross sections lithofacies maps and a paleotopographic map of the sub smackover transgressive surface shows that the distribution of lithofacies within the tst was strongly controlled by two types of sub smackover paleotopographic highs 1 norphlet dune fields and 2 eroded basement rock as th tst became progressively buried during deposition distribution of lithofacies within the hst and the smws was controlled less by these early paleotopographic features and more by 1 differential compaction around shoal water facies in the tst 2 early louann salt movement 3 basement related faulting and 4 freshwater influx along the basin rim

the oligo miocene qom formation iran evidence for an early burdigalian restriction of the tethyan seaway and closure of its iranian gateways in the central iranian esfahan sirjan and qom basins sedimentation of the oligo miocene qom formation took place on extensive mixed carbonate siliciclastic ramps during this time both basins were positioned at the eurasian margin of the tethyan seaway which connected the western and eastern regions of the tethys ocean at least until the late burdigalian during the so called terminal tethyan event the tethyan seaway was then closed due to the collision of the african arabian and iranian eurasian plates facies analysis of the sedimentary record of both basins indicates paleoenvironments ranging from terrestrial to open marine settings including mangrove restricted inner shelf lagoon seagrass meadow reefal and deeper offshore environments recognition of eight depositional sequences and elaboration of an integrated biostratigraphic framework calcareous nannoplankton planktic and larger benthic foraminifers gastropods and pectinids allow us to construct a basin spanning stratigraphy the assignment of the recognized sea level lowstands to the ru 3 to bur 3 lowstands of the global sea level curve enables a comparison with time equivalent sections from the zagros basin which was part of the african arabian plate on the opposing southern margin of the tethyan seaway the so calibrated sections display restrictions of the tethyan seaway and interruption of the south iranian gateways between the qom basin and the proto indopacific in relation to ongoing plate collision during the early burdigalian

comparison of covalently bound aliphatic biomarkers released via hydropyrolysis with their solvent extractable counterparts for a suite of kimmeridge clays abstract fixed bed hydropyrolysis at pressures greater than 10 mpa has the unique ability to maximise the yields of covalently bound alkanes without adversely affecting their stereochemistries in order to compare the yields and compositions of the solvent extractable and kerogen bound hopanes and steranes for source rocks of varying maturity six kimmeridge clay samples jurassic type ii kerogen have been subjected to successive dichloromethane extraction and hydropyrolysis the ratios of free to kerogen bound aliphatic biomarkers increase markedly at relatively low vitrinite reflectance ca 0 45 0 50 with large reductions occurring in the concentrations of bound hopanes and steranes however the fact that the total concentrations of observable hopanes and steranes i e free plus kerogen bound do not decrease until the vitrinite reflectance is greater than ca 0 50 provides evidence that neither oil migration nor aromatisation has begun to occur to a significant extent below this maturity level to the authors knowledge this represents the first study to observe a systematic change in epimer ratios with increasing maturity for hopanes and steranes covalently bound in kerogens indeed the kerogen bound hopanes and steranes undergo the same epimerisation reaction pathways as their free counterparts in the bitumen but they are generally less mature in terms of isomerisation at both ring and side chain chiral centres indeed the range of the moretane hopane index for the hydropyrolysis oils is much larger than that for the bitumens ca 5 times indicating a much greater sensitivity to relatively small changes in maturity the covalently bound hopanes and steranes released via hydropyrolysis have enabled the maturity of a contaminated core from the north sea central graben maturity to be assessed and have showed that it is compatible with the kimmeridge formation

eolian topography as a control on deposition incorporating lessons from modern dune seas permian cedar mesa sandstone se utah u s a abstract the dominant current model for the accumulation of eolian strata in the rock record emphasizes translation and climb of bedforms and the preservation of continuous beds studies of modern dune fields however show that when large dunes form they create a topographically irregular surface later episodes of eolian activity commonly fill the low lying areas between the older dunes resulting in beds that are laterally discontinuous strata in part of the permian cedar mesa sandstone in southeastern utah require this model in this new model inherited eolian topography influences subsequent deposition detailed gps mapping of an 8 km2 area was used to trace eolian strata through a 20 25 m thick unit in the cedar mesa sandstone the unit is bounded above and below by subparallel erosion surfaces that have up to 5 m of relief within the unit large transverse draa or megadune deposits are spaced 1 km apart locally over 0 5 km wide areas the draa deposits fill the entire 25 m thickness of the unit only to be completely replaced by interdraa deposits a few hundred meters away the draa surfaces were eroded and exposed prior to the filling of the intervening lows with alternations of barchanoid dune deposits sand sheets and ponds which formed in the topographic lows the cedar mesa sandstone illustrates aggradation wherein the important factor is the preserved eolian topography the draas formed an undulating stable surface from which subsequent deposition filled the interdraa low large eolian dunes that influenced subsequent deposition are also observed in several pleistocene to recent dune seas this mechanism offers an alternative to the existing models that require continuous migration of large dunes

rhodolith assemblages from the lower tortonian carbonate ramp of menorca spain environmental and paleoclimatic implications abstract lower tortonian distally steepened carbonate ramp of menorca mostly consists of foramol and rhodalgal facies deposited in inner middle ramp ramp slope and outer ramp settings red algae are abundant from the middle ramp to the lower part of the slope and their taxonomic assemblages are clearly related to the bathymetric position melobesioids percentage increases basinward passing from 55 8 in the middle ramp to 97 in the toe of slope mastophoroids are more abundant in the middle ramp 43 1 and decrease toward deeper paleoenvironments 1 2 lithophylloids and sporolithaceans appear as accessory components from the middle ramp to slope settings the percentage of melobesioids and mastophoroids observed in the middle ramp suggest that growth of the rhodoliths started in a water depth below 10 20 m the deepest occurrence of the rhodoliths is in the ramp slope environment where the dominance of melobesioids and the low percentage of shallower water subfamily suggests a water depth range of 70 to 100 m shape and structure of rhodoliths are indicative of high energy conditions in all ramp settings and they do not reflect a decrease in hydrodynamic energy related to water depth increase these conditions are related to the presence of unidirectional currents that produced cross bedded grainstones existing in the middle ramp ramp slope and at the toe of the ramp slope settings the high percentage of mastophoroids in the shallowest environments and the presence of lithoporella and sporolithon in the coralline assemblages suggests that carbonate production took place in tropical waters

hydrocarbon compositions of bitumens associated with igneous intrusions and hydrothermal deposits in britain abstract the possible modes of formation and thermal history of various palaeozoic and precambrian bitumens associated with hydrothermal deposits and igneous intrusions have been evaluated by molecular organic geochemistry the aliphatic hydrocarbon compositions of extracts of such bitumens from a number of localities have been determined by gc and gc ms procedures the stereochemical configurations and low abundance of their steranes hopanes and degraded hopanes resemble those characteristic of various mature weathered and biodegraded crude oils comparisons of the distributions of tricyclic terpanes hopanes demethylated hopanes 8 14 secohopanes and steranes reveals a close correspondence between all the bitumens from the welsh borderlands correlations suggestive of a common source rock the occurrence and abundance of 8 14 secohopanes in the bitumens is consistent with their generation as thermal degradation products of hopanes a similar mode of formation is proposed for the other unidentified secohopane in a bitumen from the midland valley of scotland overall the hydrocarbon compositions of the bitumens are compatible with their ultimate biological origins and subsequent thermal experience

families of miocene monterey crude oil seep and tarball samples coastal california biomarker and stable carbon isotope ratios were used to infer the age lithology organic matter input and depositional environment of the source rocks for 388 samples of produced crude oil seep oil and tarballs to better assess their origins and distributions in coastal california these samples were used to construct a chemometric multivariate statistical decision tree to classify 288 additional samples the results identify three tribes of 13c rich oil samples inferred to originate from thermally mature equivalents of the clayey siliceous carbonaceous marl and lower calcareous siliceous members of the monterey formation at naples beach near santa barbara an attempt to correlate these families to rock extracts from these members in the nearby cost continental offshore stratigraphic test ocs cal 78 164 well failed at least in part because the rocks are thermally immature geochemical similarities among the oil tribes and their widespread distribution support the prograding margin model or the banktop slope basin model instead of the ridge and basin model for the deposition of the monterey formation tribe 1 contains four oil families having geochemical traits of clay rich marine shale source rock deposited under suboxic conditions with substantial higher plant input tribe 2 contains four oil families with traits intermediate between tribes 1 and 3 except for abundant 28 30 bisnorhopane indicating suboxic to anoxic marine marl source rock with hemipelagic input tribe 3 contains five oil families with traits of distal marine carbonate source rock deposited under anoxic conditions with pelagic but little or no higher plant input tribes 1 and 2 occur mainly south of point conception in paleogeographic settings where deep burial of the monterey source rock favored petroleum generation from all three members or their equivalents in this area oil from the clayey siliceous and carbonaceous marl members tribes 1 and 2 may overwhelm that from the lower calcareous siliceous member tribe 3 because the latter is thinner and less oil prone than the overlying members tribe 3 occurs mainly north of point conception where shallow burial caused preferential generation from the underlying lower calcareous siliceous member or another unit with similar characteristics in a test of the decision tree 10 tarball samples collected from beaches in monterey and san mateo counties in early 2007 were found to originate from natural seeps representing different organofacies of monterey formation source rock instead from one anthropogenic pollution event the seeps apparently became more active because of increased storm activity

constraints on palaeodrainage evolution induced by uplift and exhumation on the southern flank of the zagros iranian plateau foreland sedimentary rocks from the northern fars region of iran contain a record of deformation associated with the cenozoic collision between arabia and eurasia that resulted in formation of the zagros orogen the timing of the deformation associated with this event is poorly known to address this we conducted a study of miocene foreland sedimentary rocks 19 7 14 8 ma of the chahar makan syncline using clast composition clay mineralogy and low temperature fission track dating the results showed that most of the sedimentary rocks were sourced from ophiolitic rocks detrital apatite fission track aft age signatures of miocene sedimentary rocks record exhumation in the hanging wall of the main zagros thrust and confirm that the change from underthrusting of the stretched arabian margin to widespread crustal thickening and deformation in the zagros region is no younger than 19 7 ma a transition from late oligocene to mesozoic eocene aft detrital age signatures between 19 7 16 6 ma and 16 6 13 8 ma is interpreted to reflect a possible rearrangement of palaeodrainage distribution that resulted from folding and expansion uplift of the zagros iranian plateau region supplementary material details of the succession of the study area a complete presentation of sample preparation and fission track age measurements of apatite grains and examples of x ray diffractograms are available at http www geolsoc org uk sup18502

oxygen isotopes sea level changes and the temperature history of a coral reef environment in new guinea over the last 105 years abstract coral reef terraces consisting of an upward succession of fringing and barrier reef types are preserved on land along the raising coast of huon peninsula new guinea seven coral reef units i vii from the coast landwards spaced at about 20 kyr interval provide a rather complete record of sea levels oxygen isotopes and temperature of teh surface tropical ocean over the duration of the high sea level events of the last glacial cycle the systematic sampling of the coral reefs was restricted to the massive tridacna gigas species the giant clam which are about 0 7 0 enriched in 18o relative to calcite equilibrium value and the presence of symbionts seems to have no effect on the 18o of their aragonitic skeleton sea levels rose rapidly to 5 6 5 m above present during the last interglacial which on stratigraphic grounds and 18o compositions can be separated into an early phase whose 18o is similar to modern reef viia dated at 138 kyr and a late phase that is 0 6 0 heavier reef viib dated at 118 kyr fringing reefs vi v iv iii and ii record short lived high sea levels stands at 107 85 60 45 to 40 and 31 kyr respectively that stopped short of the present sea level 12 19 28 32 to 42 m the general decline of the high sea level stands corresponds to an average 18o enrichment of 1 7 0 measured between the early interstadials of isotope stage 5 vi and v and the late interstadials of isotope stage 3 iv iiia iiib and ii the maximum 18o enrichment of 1 7 0 relative to present was registered during a regressive phase of reef iiia stratigraphic evidence indicates that sea level lows in the range of 37 to 55 m below present have occurred in between the high sea level stands but those are unlikely to represent the lowest sea levels of the last glacial cycle sea levels and 18o ddta pair offer important clues regarding the partitioning of ice volume and temperature in 18o records the results suggest that the ice volume effect accounts for the observed 18o changes during the early interstadial culminations but only for 29 46 during the late interstadial culminations sea water cooling beyond the threshold limit of coral reef growth 18 c did not occur during the last glacial cycle the temperature of the surface tropical ocean was similar to present during the early interstadials of isotope stage 5 and cooler by 3 c below present during the later interstadials of isotope stage 3

carbon isotopic compositions of 28 30 bisnorhopanes and other biological markers in a monterey crude oil abstract an immature tar like oil api 3 13 c 23 6 vs pdb from the miocene monterey formation offshore california was selected for a study of carbon isotopic signatures of individual biomarkers the three principal stereoisomers of 28 30 bisnorhopane c 28 have within analytical precision identical carbon isotopic compositions average 13 c 32 3 0 4 and are considerably depleted in 13 c compared to the whole oil these 28 30 bisnorhopanes bnh differ isotopically from c 29 and c 30 17 h hopanes 25 8 and 26 1 and c 31 c 35 extended hopanes 13 c 27 7 and suggest different precursors for the c 28 hopanes than for c 29 c 35 hopanes the relative depletion of bnh of almost 9 compared to the isotopic composition of the whole oil suggests that these hopanes derive from chemoautotrophic bacteria possibly not yet identified h 2 s oxidizers which utilize 13 c depleted substrates the c 29 and c 30 hopanes are within analytical precision isotopically identical 26 and similar to algal derived compounds e g c 27 steranes 25 9 which is consistent with a cyanobacterial source for these hopanes an archaebacterial biomarker 1 1 biphytane 13 c 25 5 likely derived from methanogens is also isotopically similar to c 27 sterane norpristane pristane and phytane liberated by desulfurization of the aromatic and polar maltene fractions show isotopic compositions similar to the same isoprenoids in the free lipids of the bitumen total range from 24 5 to 27 5 this isotopic similarity supports a common origin for the free and sulfur bound forms of these isoprenoids this origin could be algal and or archaebacterial lipids which both show isotopic compositions within the range of the c 18 c 20 isoprenoids like other marine derived organic matter this monterey oil does not show the strong 13 c depletion typical for methylotroph derived compounds characteristically found in organic matter of lacustrine origin this may indicate fundamental differences of methane recycling processes in marine sulfate dominated as compared to lacustrine environments

effects of thermal maturity on biomarker distributions in gondwana coals from the satpura and damodar valley basins india abstract organic geochemistry of gondwana coals especially the distribution of molecular fossils or biomarkers is not well constrained throughout the world in this study we have therefore evaluated biomarker signatures along with bulk organic matter and petrographic characteristics in coal samples collected from two gondwana basins in india satpura basin kanhan coalfield and damodar valley basin jharia coalfield from both coalfields the samples were collected from the lower permian barakar formation which is one of the major coal bearing strata in india a significant variation in thermal maturity levels in the samples is indicated by rock eval pyrolysis and petrographic analysis with the kanhan samples generally belonging to immature to early mature stage while the jharia samples display characteristics of overmature coals this variation in the thermal maturity strongly affects the biomarker distributions especially the terpenoids hopanes and steranes were considerably degraded due to thermal maturation and were below detection limit in the overmature samples presence of aliphatic diterpanes ent 16 h kaurane 16 h phyllocladane as well as aromatic diterpanes retene methylretenes tetrahydroretene simonellite and bisnorsimonellite in low maturity samples indicate terrestrial input possibly from the primitive conifers however the aliphatic and aromatic diterpanes were below detection limit in overmature samples making it difficult to infer their source distributions of polycyclic aromatic hydrocarbons pahs are also controlled by thermal maturity levels as evident from difference in pah ratios in the low and high maturity samples

unusual biological marker geochemistry of oils and possible source rocks offshore beaufort mackenzie delta canada abstract tertiary oils and source rocks from the offshore beaufort mackenzie delta have been examined for their biological marker content the triterpane and sterane distributions suggest a predominant land plant contribution to the oils the oils range in maturity from extremely immature to moderately mature 18 h oleanne is a major triterpane of the oils together with probable bisnorlupanes and an excellent correlation is observed in the concentration of these components in individual oils an excellent correlation is also observed between the concentration of bisnorlupanes and oil maturity based on sterna and triterpane maturation parameters suggesting that the decrease in relative concentration of these components with increasing maturity is a result of progressive dilution by hydrocarbons generated by the cracking of kerogen only one formation in cores taken from the delta has been found to contain bisnorlupanes and were present they are the dominant hydrocarbons of the branched cyclic fraction

c26 and c28 c34 28 norhopanes in sediments and petroleum abstract a complete series of 28 norhopanes c26 and c28 c34 has been detected in oil samples and rock extracts from west greenland and the north sea only the c28 members of the series 28 30 bisnorhopanes and the related 25 28 30 trisnorhopanes have been described in the literature 28 30 bisnorhopanes are often the only 28 norhopanes in oils and sediments and their isotopic composition can be different from that of the regular hopanes suggesting that 28 30 bisnorhopanes have a different origin in other cases 28 norhopanes and regular hopanes have a similar distribution of homologues and there is no isotopic evidence for a different origin of the two series when the complete series of 28 norhopanes is present it is usually accompanied by high concentrations of the corresponding demethylated aromatic 8 14 secohopanes the 28 norhopanes seem to be less resistant to biodegradation than regular hopanes and there is a preferential demethylation of the low molecular weight 28 norhopanes c25 and c27 c31 25 28 bisnorhopanes have been identified in biodegraded oils the c28 c34 28 norhopanes are best studied using the m z 355 mass chromatogram since this fragment is comparatively intense and the interference from other compounds is usually low the 17 h 21 h 17 h 21 h 17 h 21 h ratios of the c29 and c30 28 norhopanes can be used as maturity parameters in immature samples a large proportion of the 28 norhopanes especially c28 and c30 occurs in the bitumen however hydrous pyrolysis experiments have shown that 28 norhopanes are also part of the kerogen

global and local controls influencing the deposition of the la luna formation cenomanian campanian western venezuela bulk and molecular geochemical micropalaeontological and carbon isotopic data are used to address the different local and global factors influencing the environment of sedimentation of the la luna formation cenomanian campanian approximate palaeolatitude 15 n in a single section in western venezuela based on the constructed chronostratigraphic framework oxygen depleted bottom water conditions and black shale deposition started in western venezuela well before the widespread occurrence of organic rich sediments in higher palaeolatitude regions such as the tethys and the north atlantic near or at the cenomanian turonian boundary in the la luna formation palaeoenvironmental conditions that allowed the preservation of organic matter mainly of marine origin prevailed until santonian times in a distal platform facies with very low siliciclastic input changes in lithology appear to reflect the local response to eustatic sea level variations and the presence of a migrating upwelling belt affecting the bioproductivity of silica and carbonate a marked 13corg isotopic excursion is recognised in the middle part of the section and is apparently unrelated to local palaeoenvironmental changes in bioproductivity and oxygen depletion biological marker data show no variations in association with the isotopic excursion being mainly controlled by local fluctuations in organic matter input and preservation

micropalaeontological and geochemical evidence of mid cretaceous dysoxic anoxic palaeoenvironments in the sergipe basin northeastern brazil

origin of petroleum in the neoproterozoic cambrian south oman salt basin abstract the south oman salt basin sosb is host to the world s oldest known commercial deposits most of the south oman oils have been proven to be associated with the source rocks of the neoproterozoic to cambrian huqf supergroup but the assignment of oils to specific huqf intervals or facies has been hampered by the geochemical similarity of the organic matter across the entire huqf sequence possibly as a consequence of limited change in the local palaeoenvironment and biota over the time of its deposition this study was conducted to establish improved correlations between organic rich rock units and reservoir fluids in the sosb through detailed molecular and isotopic analysis of the huqf supergroup with special emphasis directed towards understanding the ara carbonate stringer play unusual biomarkers tentatively identified as a norsteranes show distinctive patterns among carbonate stringer oils and rocks different from those observed in nafun sediments and ara rocks from the athel basin these putative a norsteranes form the basis for new oil source correlations in the sosb and provide for the first time geochemical evidence of a self charging mechanism for the carbonate stringer play the paucity of markers specific to the nafun group shuram buah and masirah bay formations confounds attempts to quantify their respective contributions to huqf oil accumulations nafun inputs can only be determined on the basis of subtle differences between nafun and ara biomarker ratios the most useful geochemical characteristics delineating nafun group organic matter from ara group intra salt source rocks included low relative abundance of mid chain monomethyl alkanes x compounds low relative abundance of gammacerane 28 30 dinorhopane 25 28 30 trinorhopane and 2 methylhopanes low c 22 t c 21 t and high c 23 t c 24 t cheilanthanes ratio values based on these parameters molecular evidence for major contributions of liquid hydrocarbons from nafun group sediments shuram buah and masirah bay formations is lacking our results suggest that the majority of sosb hydrocarbon accumulations originate from within the ara group either from the carbonate stringers or from the package of sediments that comprises the thuleilat athel silicilyte and u shale formations subtle aspects of the composition of some carbonate stringer and post salt huqf oils could suggest some degree of sourcing from the nafun rocks but stronger evidence is needed to confirm this

oligocene and early miocene coral faunas from iran palaeoecology and palaeobiogeography oligocene and early miocene coral assemblages from three sections of central iran are investigated with respect to their palaeoecological and palaeobiogeographic implications these corals are compared with faunas from the mediterranean tethys and the indopacific associated larger foraminifers are used for biostratigraphy and to support the palaeoecological interpretation the studied sections are situated in the foreland basins of the iranian plate which is structured into a fore arc and a back arc basin separated by a volcanic arc the coral assemblages from abadeh indicate a shallowing upward trend infrequently distributed solitary corals at the base of the section indicate a turbid environment above a distinct horizon characterised by a leptoseris stylophora assemblage associated with lepidocyclinids and planktonic foraminifers is interpreted as maximum flooding surface small patch reefs with a porites faviidae assemblage are a common feature of late oligocene to early miocene coral occurrences and indicate water depths of less than 20 m the diversity of the coral faunas shows marked differences oligocene corals from the esfahan sirjan fore arc basin comprise more than 45 species of 32 genera and occur in a wide range of environments early miocene corals from the qom back arc basin are less frequent show a lower diversity 13 genera with 15 species and occur in single horizons or small patch reefs

dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum abstract the steroidal alkanes of a selection of sediments and oils have been examined by gc ms with multiple metastable reaction monitoring specific 4 methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates an immature marine oil shale and two mature marine oils of triassic to early cretaceous age contained high concentrations of c30 steranes comprising desmethyl 24 ethyl 4 methylcholestane and 4 23 24 trimethylcholestane dinosterane isomers an immature non marine oil shale and two non marine oils of cretaceous to eocene age contained stereoisomers of 24 ethyl 4 methylcholestane as the dominant c30 steranes reaction monitoring analyses in gc ms are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks

meco and alpine orogenesis constraints for facies evolution of the bartonian nummulitic and solenomeris limestone in the argentina valley ligurian alps

oil oil and oil source rock correlations in the carpathian foredeep and overthrust south east poland abstract the chemical composition of 35 crude oils and the extracts of potential source rock samples from south east poland were studied in detail by geochemical methods in order to understand their genetic relationships twenty six oils including three seep samples were collected from cretaceous to oligocene reservoirs within the carpathian overthrust nine oils originated from carboniferous to miocene reservoirs within the carpathian foredeep the rock samples studied were selected after rock eval pyrolysis screening of a large suite of samples and consist of one lower cretaceous sample and five oligocene menilite shale samples from three different outcrop locations all within the carpathian overthrust geochemical fingerprinting indicates at least two families of crude oils the first represented only by one oil has no specific characteristics except for a light carbon isotope composition the second family is characterized by the presence of 28 30 dinor hopane oleanane and a highly branched isoprenoid c25 alkane within this latter family four subfamilies were recognized a 19 oils having the aforementioned characteristics b seven oils similar to subfamily a but with a relatively high sulphur content c one oil with high abundance of higher plant derived triterpanes and d seven oils with abundant 28 30 dinor hopane although maturity influences the relative abundance of 28 30 dinor hopane it suggested that subfamilies a b and c had an initial low 28 30 dinor hopane content whereas subfamily d an initial high 28 30 dinor hopane content only one oil of subfamily a could potentially be a high maturity counterpart of subfamily d a palaeozoic source rock is suggested for the first family and the second family including the majority of the pils from the carpathian foredeep is most likely derived from the oligocene menilite shales an oil source rock relationship with the menilite shale is supported by the presence although not in all samples studied of 28 30 dinor hopane oleanane or its precursors and the highly branched isoprenoid alkane the strong facies variations observed within this shale gave rise to the different types of crude oils in the second family

geochemical comparison of fluid inclusion and present day oil accumulations in the papuan foreland evidence for previously unrecognised petroleum source rocks abstract petroleum production in papua new guinea is limited to the papuan fold belt present day oil accumulations in fields such as iagifu hedinia and gobe are thought to be mainly derived from clay rich jurassic marine source rocks containing terrestrially derived organic matter that were deposited under oxic conditions in this study other generative source rocks in the papuan foreland are indicated using fluid inclusion fi oil data from three wildcat wells koko 1 bujon 1 and kimu 1 which were drilled on the bosavi arch detailed organic geochemistry of these fi oils and associated free oils or oil stains suggests that none of these were generated from the aforementioned jurassic source rocks instead at least three different generative source rocks are indicated firstly a marine probably late cretaceous or younger source rock deposited under reducing conditions is indicated by the bujon 1 fi oil this source rock had a moderate contribution from higher plant organic matter including oleanane and or lupane the bujon 1 fi oil has similarities with fi oils from the iagifu 7x and p nyang 2x wells in the papuan fold belt secondly an algal dominated lacustrine source rock is indicated by the biodegraded koko 1 rft crude oil the unbiodegraded fi oil from koko 1 and the bujon 1 oil stains from the toro and imburu formations these lacustrine oils have high abundances of tricyclic terpanes pregnane homopregnane and gammacerane contain carotane and have high c26 c25 tricyclic terpane ratios the source of the lacustrine oils is inferred to contain moderate amounts of terrestrial organic matter indicated by a dominance of c29 steranes and abundant aromatic higher plant biomarkers and could be gypsiferous shales embedded in oligocene miocene carbonates or triassic age sediments deposited on igneous basement during early rifting associated with the break up of gondwana the kimu 1 fi oil was generated from a mature marine suboxic source rock but has a different geochemical composition to free oil from a similar interval which was derived from a carbonate rich source rock none of the fi oils correlate well with oil families previously described in papua new guinea accordingly the oils recovered from fis in this part of the papuan basin support the presence of laterally varying source rock compositions and qualities and indicate that there are opportunities to develop new charge models for features across the papuan foreland furthermore koko 1 bujon 1 and kimu 1 fi oils have different geochemical compositions compared to the associated free oils or oil stains indicating that each of these localities has a multi phase charge history further work to lower exploration risk in the papuan foreland should be directed to understanding the distribution maturity and expulsion history of these newly recognised potential source rocks

lower tertiary and upper cretaceous source rocks in louisiana and mississippi implications to gulf of mexico crude oil the lower tertiary sparta formation wilcox group and the midway group in southern louisiana include organic rich source facies that generate crude oil at relatively high thermal maturities the wilcox group is an important source of wilcox crude oil and regional kerogen variations explain two crude oil subfamilies wilcox crude oils in downdip areas of southern louisiana migrated short distances but long range lateral migration about 150 km best explains wilcox crude oils far updip from mature source rocks crude oils in oligocene and younger reservoirs in southern louisiana migrated vertically from deep lower tertiary source rocks some crude oils in upper cretaceous tuscaloosa reservoirs were emplaced by long range lateral migration from tuscaloosa source rocks g ven little evidence of upper tertiary source rocks and the overmaturity problems of mesozoic source rocks most crude oils in upper tertiary and pleistocene reservoirs of the gulf continental shelf are best explained by vertical migration from deep lower tertiary source rocks even so it is simplistic to assume an exclusive lower tertiary origin many tertiary and pleistocene crude oils of this study probably include an overprint of high maturity hydrocarbons from mesozoic sources

paleobiogeography of scleractinian reef corals changing patterns during the oligocene miocene climatic transition in the mediterranean abstract during the oligocene miocene greenhouse to icehouse climatic transition the biogeography of reef corals or zooxanthellate like scleractinian corals was gradually changing from a pan tropical tethyan province in the eocene to three reef coral provinces of the western atlantic caribbean indo pacific and mediterranean our reefcoral database encompasses updated and homogenized data on paleoenvironmental and systematics of scleractinian corals occurring in the oligocene and miocene outcrops from circum mediterranean regions provided by most of relatively recently published data in the literature and by the study of published and unpublished collections of coral specimens from the same area including the important collections housed at the mnhn paris and our own collections as there is no validated direct criterion for the identification of the coral zooxanthellate symbiosis in the fossil record and considering the difficulty to use the biogeochemical approaches in the context of this study the subjectivity of the morphological criteria and the relative recent age of the fossil corals we are dealing with a uniformitarian approach has been used for inferring the symbiotic status of scleractinian genera in reefcoral among the 158 genera included in our database 93 can be considered as zooxanthellate and 10 have a doubtful zooxanthellate status this relatively exhaustive database was used to reconstruct the temporal and spatial distribution of scleractinian corals in the mediterranean during the oligocene miocene time in order to discuss the interplaying effects of the global cooling at that time the re organization of the tethyan realm resulting from the african arabian and eurasian plate collision and the emergence of the alpine chains driving the gradual northward movement of the whole region outside the tropical subtropical belt it is shown that the structure of the mediterranean z coral oligocene miocene paleobiodiversity was characterized by many geographically restricted genera with a moderate to short stratigraphical range and a few long ranging widespread genera a major consequence of this structure is that the extinction pattern has proceeded through the preferential extinction of rare occurrence genera through time the potential rapid long distance dispersal of most coral larvae compared to the size of the oligocene miocene mediterranean explains why no biogeographical subprovinces can be distinguished for the z coral fauna on a local scale ecological processes tend to sort coral taxa by limiting z coral development to geographically restricted and discontinuous areas this accounts for the large amount of geographically restricted taxa forming the mediterranean coral fauna the interaction of plate tectonics alpine orogenesis and climate at local to subregional scales exerts strong controls over the spatio temporal distribution of z coral assemblages within the circum mediterranean realm in particular we suggest that the richness and composition of the eastern atlantic coral fauna are indirectly related to the opening and closure of the eastern seaway connection with the indian ocean which controlled the e w circulation of surface waters and hence the westwards dispersal of pelagic larvae at the scale of the whole region the gradual regional climatic change produced by the northwards migration of the entire area superimposed on the global cooling appears in large part responsible for the extinction pattern of z corals through time in the mediterranean biogeographical province

organic geochemistry of dsdp site 467 offshore california middle miocene to lower pliocene strata abstract results of the analyses of twenty three samples from the middle miocene to lower pliocene strata from dsdp site 467 offshore california are presented the analyses were performed with the aim of determining the origin of the organic matter the stratigraphic section s hydrocarbon generation potential and extent of organic diagenesis organic carbon contents are an order of magnitude greater than those typically found in deep sea sediments suggesting an anoxic depositional environment and elevated levels of primary productivity hydrocarbon generation potentials are above average for most samples the results of elemental analyses indicate that the kerogens are primarily composed of type ii organic matter and are thermally immature analysis of the bitumen fractions confirms that the samples are immature in cores from 541 to 614 meters the gas chromatograms of the c 15 non aromatic hydrocarbon fractions are dominated by a single peak which was identified as 17 h 18 h 21 h 28 30 bisnorhopane this interval is the same area in which the highest degrees of anoxia are observed as reflected by the lowest pristane phytane ratios this correlation may have some implications with regard to the origin of the bisnorhopane and its possible use as an indicator of anoxic depositional conditions within thermally immature sediments

tertiary sequence of deformation in a thin skinned thick skinned collision belt the zagros folded belt fars iran 1 we describe how thin skinned thick skinned deformation in the zagros folded belt interacted in time and space homogeneous fold wavelengths 15 8 5 3 km tectono sedimentary evidence for simultaneous fold growth in the past 5 5 2 5 ma drainage network organization and homogeneous peak differential stresses 40 15 mpa together point to buckling as the dominant process responsible for cover folding basin analysis reveals that basement inversion occurred 20 ma ago as the arabia eurasian plate convergence reduced and accumulation of neogene siliciclastics in foreland basin started by 10 ma ongoing contraction occurred by underplating of arabian crustal units beneath the iranian plate this process represents 75 of the total shortening it is not before 5 ma that the zagros foreland was incorporated into the southward propagating basement thrust wedge folds rejuvenated by 3 2 ma because of uplift driven by basement shortening and erosion since then folds grew at 0 3 0 6 mm yr and forced the rivers to flow axially a total shortening of 65 78 km 16 19 is estimated across the zagros this corresponds to shortening rates of 6 5 8 km ma consistent with current geodetic surveys we point out that although thin skinned deformation in the sedimentary cover may be important basement involved shortening should not be neglected as it requires far less shortening moreover for such foreland folded belts involving basement shortening underplating may be an efficient process accommodating a significant part of the plate convergence

the petroleum geochemistry of canadian beaufort tertiary non marine oils abstract molecular isotopic and elemental data for a set of 28 paleogene and 3 cretaceous oils from the mackenzie delta and offshore canadian beaufort sea have been evaluated the depositional environment and organic matter characteristics of the source units for these oils have been predicted the paleogene oils of the canadian beaufort are molecularly distinctive and clearly contain a major land plant component oleanane and the 17 h and 17 h 24 28 bisnorlupanes are present as well as the following compound types 24 norlupanes and possibly higher homologues de a lupane noroleanenes norursene dehydroabietane 28 30 bisnorhopanes several molecular and isotopic characteristics are useful in assessing and ordering the extent of biodegradation and thermal maturation of these oils the cretaceous oils are separately sourced from the paleogene oils the latter oils comprise two distinct land plant derived genetic families distinguished by the presence absence of 24 28 bisnorlupanes 24 norursene 24 norlupane and 24 noroleanenes the kugmallit richards family contains each of these compound types and is considered to originate from the eocene richards formation in contrast lupanoids and noroleanenes are absent in oils of the reindeer moose channel family the occurrence of 28 30 bisnorhopane and or oleanane in these oils suggests a paleocene origin although these source rock predictions are supported by the available data they must be considered speculative until detailed molecular isotopic and elemental compositional data are available regionally for potential source rocks of the eocene and paleocene source units in the canadian beaufort

compound specific isotope analysis as a tool for characterizing mixed oils an example from the west of shetlands area abstract the origin of an oil accumulation can be difficult to establish when the oil is a mixture from multiple sources or when multiple episodes of charging are involved in this study oils from the clair field west of shetland islands which are mixtures of nonbiodegraded oil added to biodegraded oil are characterized by comparing the carbon isotope ratios of the gasoline range hydrocarbons grh of the oil to the grh released from the pyrolysis of the asphaltenes in the oil this comparison allows characterization of the source of the first versus the second pulse of oil into the reservoir information useful in assessing the source potential of the basin

biogeographic constraints for tectonic reconstructions of the pacific region suspect terranes in western north america contain permian and triassic genera that were endemic to the tethyan region trend surface analysis of modern biogeographic data constitutes a new approach to understanding the origin of these exotic faunas we use the generic diversity of living reef corals together with paleomagnetic results from quaternary lavas to calculate the present locations of easter island hawaii and tahiti the results demonstrate that the eastward decline in coral diversity may be used as a measure of longitude similar data from the fossil record should constrain paleogeographic reconstructions of the pacific region

production and cycling of calcium carbonate in a shelf edge reef system st croix u s virgin islands applications to the nature of reef systems in the fossil record abstract geologic reefs are the end products of not only constructive processes that produce calcium carbonate but also of destructive processes e g bioerosion and wave action that reduce solid substrate to sediment and of physical processes that rework the reef fabric and transport sediment a study was conducted at cane bay on the island of st croix u s virgin islands to quantify the suite of processes that have influenced holocene reef development data on carbonate production reef accretion bioerosion and sediment transport were used to construct a detailed carbonate budget and to apply the findings of this study to the character of reefs observed in the fossil record total carbonate production on the reef ranged from 0 to 5 78 kg m2 per year with a reef wide average of 1 21 kg m2 per year 1 13 by corals 0 02 by coralline algae 0 06 by primarily molluscs forams and echinoderms based on 7 cores only 0 91 kg m2 per year of this have been retained within the reef interior the remaining 0 24 kg m2 per year of sediment along with the 0 06 kg m2 per year contributed directly by molluscs etc are deposited within reef channels and are probably flushed from the reef by major storms of the material recovered in the cores 58 was either loose sediment and rubble or open void space much of the recognizable coral material was demonstrably reworked and out of place accretion rates across the shelf generally increased with water depth as a result of active slumping along the steepening reef face over the past 2 000 3 000 years the importance of detrital material in the reef fabric and the major role played by secondary processes that constantly rework the substrate have resulted in a reef whose interior is more of a garbage pile than an in place assemblage of corals cemented together into a rigid framework the physical similarities between the detrital fabric of the reef at cane bay and those found in many ancient deposits imply that the general processes operating along the cane bay shelf have persisted during much of the evolution of ancient reefs it is proposed that our modern models overemphasize the importance of in place framework as a criterion for an ecologic reef

estimating mediterranean oligocene miocene sea surface temperatures an approach based on coral taxonomic richness abstract during the oligocene and miocene shallow water carbonates of the mediterranean region were rich in scleractinian corals thriving within various depositional settings including different reef types their diversity patterns although related to a complex interplay between a suite of environmental factors and palaeobiogeography are considered to be strongly controlled by climate variability and changes in sea surface water temperature by using the quantitative relationship between present day coral taxonomic richness and prevailing sea water temperature underlined by the so called energy hypothesis we test zooxanthellate coral generic richness values from a selection of 102 oligocene miocene localities of the mediterranean region as a proxy for relative palaeotemperatures for each oligocene miocene stage generic richness values per z coral site are firstly examined together with variations of the mediterranean z coral generic pool for better testing the method and assessing its potential application patterns of generic richness and inferred palaeotemperatures are then compared with global palaeoclimatic curves based on marine oxygen stable isotopes data or other climate proxies such as palaeoclimatic records from european continental floras and from fossil coral linear extension rate results clearly show that fluctuations of coral richness derived palaeotemperatures correspond relatively well with global changes of sea water temperature especially for the entire oligocene the chattian aquitanian boundary and the late miocene the well known mid miocene climatic optimum however is not recorded suggesting that regional factors acting together with important palaeogeographical changes exerted a strong control on the generic richness of mediterranean z coral communities a remarkable decline of taxonomic richness is recorded after the burdigalian together with a gradual decrease of palaeotemperatures in the region from the middle miocene onwards to the messinian however an increase in the temperature range of z coral localities is clearly visible indicating that z coral communities were able to thrive and adapt to a wider temperature range as the mediterranean was gradually migrating northwards outside the tropical belt the energy hypothesis if used at global or regional scale can be considered a promising and reliable method for estimating cenozoic palaeotemperatures from coral or other suitable fossil assemblages of shallow water carbonates

reef geometries erosion surfaces and high frequency sea level changes upper miocene reef complex mallorca spain the upper miocene reef complex of mallorca is a 20 km prograding unit which crops out in sea cliffs along the southern side of the island these vertical and exceptionally clean outcrops permit i identification of different facies lagoon reef front reef slope and open platform and their geometries and boundaries at different scales ranging from metre to kilometre and ii construction of a 6 km long high resolution cross section in the direction of reef progradation this cross section shows vertical shifts of the reefal facies and erosion surfaces linked to a general progradational pattern that defines the accretional units four hierarchical orders of magnitude 1 m to 4 m of accretional units are identified by consideration of the vertical facies shifts and by which erosion surfaces are truncated by other erosion surfaces all these orders show similar patterns horizontal beds of lagoonal facies in the upper part landward reefal and slope facies with sigmoidal bedding in the central part and open platform facies with subhorizontal bedding in the lower part basinwards the boundaries are erosion surfaces horizontal over the lagoon facies dipping basinwards over the reef front facies and connecting basinwards with their correlative conformities over the reef slope and open platform facies the four orders of accretional units are interpreted in terms of four 1 m to 4 m hierarchies of sea level cycles because i there is a close relation between the coral growth and the sea surface ii there are vertical shifts in the reefal facies and their relation to the erosion surfaces and iii there was very little tectonic subsidence in the study area during the late miocene additionally all these units can be described in terms of their position relative to the sea level cycle i the reefs prograde on the open platform sediments during low stands of sea level ii aggradation of the lagoon reef and open platform facies dominates during sea level rises and the lagoonal beds onlap landwards upon the previous erosion surface iii reefal progradation occurs during high stands of sea level and iv the 2 m sea level fall produces an off lapping reef and there is progradation with downward shifts of the reefal facies and erosion landward on the emerged older reefal units a erosion surfaces the 3 m and 4 m sea level falls produce only erosion b and c erosion surfaces although precise age data do not exist at present some speculations upon the frequency of these miocene relative sea level cycles can be made by comparisons with pleistocene cyclicity there is a good correlation between the miocene 2 m cycles and the 100 ka pleistocene cycles consequently the 1 m cycles can be assigned to a fourth order in relation to previously proposed global cycles and the 2 m to fifth order cycles all these accretional units could be defined as sequences according to the definition as commonly used in sequence stratigraphy however they represent higher than third order sea level cycles but are not parasequences the term subsequence therefore is suggested to define a part of a sequence bounded by erosion surfaces mostly subaerial and their correlative conformities basinwards a hierarchy of subsequences can be established

sedimentation and diagenesis of upper smackover grainstone jay field area west florida abstract the examination of core and logs from a well 3 mi 5 km southwest of the jay field has given considerable insight into the upper smackover facies distribution diagenesis and the application of recent models for the sedimentation and diagenesis of this jurassic reservoir a 63 ft 19 m thick unit of oolitic and oolite oncolite grainstones is recognized in the upper smackover high angle inclined bedding visible on both core and dipmeter with a consistent 15 to 20 northeast dip demonstrates the presence of oolite bars these bars formed a barrier which affected subsequent deposition and diagenesis in the jay field area a complicated diagenetic history of marine and vadose cementation and pervasive and selective dolomitization have left a unique imprint on the porosity and permeability of these rocks dipmeter results and petrographic analysis of the grainstones indicate that cementation and diagenesis have not been uniform within the large scale cross strata permeable beds are interstratified with tightly cemented or compacted impermeable beds horizontal flow should be greatest along the strike of the inclined units because the flow would remain within the permeable planes of the inclined strata thus dipmeter correlation permits an interpretation of the direction of bedding permeability anisotropy produced by the inclination of the pore system the characteristics of sedimentation and facies distribution in the jay field area have previously been compared with a modern analog from joulters cay in the bahamas the trucial coast of the persian gulf in the abu dhabi region may be a better model the style of deposition and distribution of carbonate and evaporite sediments and diagenetic characteristics in the grainstone barriers and lagoons closely fit the sedimentation and diagenetic pattern in the jay field area end of article last page 950

mineralogical and geochemical evidence for coupled bacterial uranium mineralization and hydrocarbon oxidation in the shashagetai deposit nw china unusual mineral structures have recently been found in a sandstone hosted roll type uranium deposit in the middle jurassic zhiluo formation in the shashagetai deposit the northern ordos basin nw china the structures possess a chemical composition and crystal structure characteristic of mineral coffinite usio4 1 x oh 4x which occurs as nanoparticles with size ranging from 5 to 25 nm these structures are interpreted to be fossilized microorganisms based on mineralogical biosignatures including morphology size occurrence of biogenic coffinite as nano crystals and biological elements such as p the intimate intergrowth of coffinite with secondary pyrite of bacterial origin as defined by low 34 s values and calcite cements with petroleum derived carbon supports its biogenic origin oil inclusions in the host sandstone are characterized by abundant n alkanes slightly increased pr nc17 and ph nc18 ratios significant amounts of demethylated hopanes and tricyclic terpanes and the existence of unresolved complex mixtures these characteristics are interpreted to be a result of mixing of an earlier heavily degraded oil with a later charged fresh oil subsequently the oils were slightly degraded these lines of evidence lead to the proposal that the reduction of sulfate and oxidization of petroleum are likely synchronous with reduction of hexavalent u vi to tetravalent u iv uranium by sulfate reducing bacteria srb the discovery of a natural association of microorganism like structures a uranium mineral and biodegraded petroleum has implications for uranium biomineralization and fossil fuel exploration

environmental evolution and geological significance of the miocene carbonates of the eratosthenes seamount odp leg 160 abstract miocene carbonates of the eratosthenes seamount located offshore from cyprus in the eastern mediterranean odp leg 160 site 966 have been re analysed the use of sedex sequential extraction to evaluate the nutrient concentrations and of ct scan for the identification of large benthic foraminifera has resulted in a more detailed palaeoenvironmental reconstruction and an improved stratigraphic framework three intervals are recognised in the succession and are attributed to the lower middle and upper miocene respectively the lower miocene interval is dominated by large benthic foraminifera and echinoids this association colonized the top of the seamount following its uplift from deep water to the photic zone the middle miocene interval is characterised by rhodoliths and corals at its base and near the top whereas seagrass seaweed assemblages with epiphytic foraminifera and hooked coralline algal crusts dominate its central part the upper miocene is represented by coral reef facies near its base and lagoonal facies toward its top the succession was deposited in an oligotrophic environment and exhibits a general shallowing upward trend that was mainly controlled by tectonic activity related to the northward subduction of the african plate the succession of the eratosthenes seamount is characterised by a diverse large benthic foraminifera assemblage in its lower part and by corals in its uppermost part whereas corallines characterise the central interval this trend is common in miocene mediterranean carbonates and its occurrence on an isolated seamount confirms its connection with the general evolution of the basin the decline of miogypsinids and lepidocyclinids after the early miocene is notable because the eratosthenes seamount was geographically close to the indo pacific ocean where both groups also thrived during the middle miocene this decline was probably caused by the early miocene closure of the deep water connection between the indo pacific and the mediterranean

comment on revision of the age of the qom formation in the central iran basin iran by zhu et al journal of asian earth sciences 2007 vol 29 715 721

migration of petroleum into vermilion 14 field gulf coast u s a molecular evidence abstract oils and condensates from vermilion 14 field offshore louisiana u s a are compared using sulfur and nitrogen concentrations whole oil carbon isotope ratios and hydrocarbon distributions all parameters suggest large differences in the organic facies of the source rock s and in thermal maturity of the source at the time of expulsion certain bulk geochemical data including n alkane distributions and whole oil carbon isotope ratios suggest that migration fractionation resulted in oils condensates whose molecular distributions are shifted significantly toward lower molecular weight components migration contamination is supported by the occurrence in the oils of unsaturated and thermally unstable hydrocarbons including oleanenes dammarenes and diasterenes and molecular maturity ratios indicative of immature organic matter molecular maturity ratios of the oils increase with increasing reservoir depth regardless of reservoir lithology or formation for example the 20s 20s 20r 5 h 14 h 17 h 24 ethylcholestane ratio increases from 0 05 to 0 58 over a depth range of 6316 ft to 15 563 ft the same ratio for cuttings extracts from two wells in the vermilion 14 field shows lower values although they also increase with increasing depth it is proposed that the vermilion hydrocarbons were generated from deep source rocks approximately 15 000 ft or more and possibly subjected to migration fractionation during movement to shallower reservoirs during migration and after trapping migration contamination added unsaturated hydrocarbons to the oils condensates resulting in anomalously low molecular maturity ratios we suggest further that the combined effects of migration fractionation and migration contamination resulted in oil in the vermilion 14 field that is compositionally different from that which initially left the deep source rock

crustose coralline algae from the flower garden banks northwestern gulf of mexico controls on distribution and growth morphology abstract the east and west flower garden banks in the northwestern gulf of mexico represent the northernmost tropical coral reefs and caribbean coralline algal flora on the north american continental shelf coralline algae are the dominant framework builders and sediment contributors below 50 m on the banks on the basis of growth form and taxonomic composition coralline algae on the flower garden banks can be divided into four overlapping depth zones upper coral reefs 20 30 m madracis algal ridges 30 40 m algal nodule zone 45 80 m and deep algal reefs 50 90 m corallines on the upper coral reefs are dominated by hydrolithon lithophyllum and porolithon their growth form as thick laterally restricted crusts and knobs results from intensive grazing by parrotfish and urchins grazing is diminished on the madracis algal ridges below the upper reefs and corallines grow here as laterally extensive plates binding coral rubble dominant corallines on the ridges are lithophyllum paragoniolithon and tenarea algal nodules rhodoliths o the deeper bank slopes are the most widespread algal growth form on the flower garden banks on the basis of shape internal structure and composition rhodoliths are divided into an upper zone where they have a spherical shape with concentric laminae and a lower zone discoidal shape with irregular laminae diminishing current velocity with increasing depth controls nodule morphology the red alga peyssonnelia and the foraminifer gypsina are two non coralline components that contribute substantially to nodule growth reduced current velocity in the lower nodule zone enables corallines and peyssonnelia to develop laterally extensive pavements and 1 2 m high algal reefs taxonomic composition high framework porosity and irregular internal growth morphology f the deep algal reefs distinguish these structures from shallow algal ridges described elsewhere the 90 m isobath at the flower garden banks approximates the upward limit of a turbid nepheloid layer composed of continually resuspended sediment reefal structures within this water layer are dead and are now covered by fine sediment

gc ms characterisation of c27 and c28 triterpanes in sediments and petroleum abstract earlier studies have shown that an unusual c 27 triterpane is abundant in sediments from the norwegian continental shelf and the north sea this compound was assigned the tentative structures 24 28 30 trisnormoretane or 25 28 30 trisnormoretane but we have now shown from detailed retention time measurements and a reinterpretation of the mass spectral data that its correct structure is 17 h 18 h 21 h 25 28 30 trisnorhopane two other triterpanes 25 28 30 trisnormoretane and 28 30 bisnormoretane have also been identified as minor constituents of extracts of sediments from the north sea possible origins for these compounds are discussed

early diagenetic transformation of higher plant triterpenoids in deep sea sediments from baffin bay abstract a sediment sequence of early miocene to holocene from ocean drilling program site 645 in central baffin bay was found to contain abundant triterpenoids of higher plant origin including monodesmethyl derivatives and other oxidative degradation products 24 nor triterpenoids of the oleanene ursene and lupane series were found in the nonaromatic hydrocarbon and alcohol fractions of the sediment extracts other diagenetic transformation products included 24 28 dinor olean 17 ene and 24 nor urs 12 en 1 1 one as well as their tentatively identified des a counterparts the identification of these novel degradation products was confirmed by synthesis of a suite of reference compounds the simple reaction sequence applied to obtain 24 nor urs 12 ene from 3 acetoxyurs 12 en 24 oic acid is likely to happen in a similar manner during early diagenesis of organic matter in nature these results have implications for the understanding of the diagenetic reaction sequence leading to the formation of other demethylated triterpenoids of terrigenous origin e g 24 28 dinor lupanes 28 30 dinor 17 hopane is sometimes the dominant hydrocarbon in the most deeply buried samples its co occurrence with higher plant triterpenoids and the low abundance of other regular hopanoids is not considered an indication however that 28 30 dinor 17 hopane is derived from a higher plant precursor molecule it is suggested that two independent sedimentary processes are responsible for the presence of the two types of demethylated triterpenoids observed in baffin bay sediments

organic geochemistry of the sedimentary basins of new zealand part iv a biomarker study of the petroleum seepage and some well core bitumens from the geothermal region of ngawha springs abstract the crude oil which seeps to the surface at ngawha springs was mature but the oil biomarker parameters indicated that its unlocated source rocks had not reached the peak of oil generation the oil had a mixed marine and terrigenous origin and had not undergone secondary migration except to the surface the oil was distinguished from diesel oil which might have polluted thermal springs in the area by several parameters specifically those which relate to the source of an oil the seep oil was concluded to have arisen from accelerated diagenesis of organic material in tertiary rocks which cap the geothermal system at ngawha a surface asphalt which had formed from the oil was lightly degraded it had absorbed hydrocarbons from immature organic matter near the surface and its hydrocarbon composition was characterised by an abundance of a 22r homohopane this triterpane was also present in rock bitumens together with appreciable proportions of hopanes bitumens extracted from potential source rocks were largely of terrigenous origin they had characteristics of sedimentary organic material which had not reached the oil generation threshold these rocks did not prove to be the source of the seep oil one of the bitumens contained a c 28 triterpane the presence of which suggested that the sedimentary organic material had been reworked by bacteria such a view was consistent with the geological history of ngawha springs

biological marker distribution in coexisting kerogen bitumen and asphaltenes in monterey formation diatomite california organic rich 18 2 monterey formation diatomite from california was studied the organic matter consist of 94 bitumen and 6 kerogen biological markers from the bitumen and from pyrolysates of the coexisting asphaltenes and kerogen were analyzed in order to elucidate the relationship between the various fractions of the organic matter while 17 alpha h 18 alpha h 21 alpha h 28 30 bisnorhopane was present in the bitumen and in the pryolysate of the asphaltenes it was not detected in the pyrolysates of the kerogen a c40 isoprenoid with head to head linkage however was present in pyrolysates of both kerogen and asphaltenes but not in the bitumen from the diatomite the maturation level of the bitumen based on the extent of isomerization of steranes and hopanes was that of a mature oil whereas the pyrolysate from the kerogen showed a considerably lower maturation level these relationships indicate that the bitumen may not be indigenous to the diatomite and that it is a mature oil that migrated into the rock we consider the possibility however that some of the 28 30 bisnorhopane rich monterey formation oils have not been generated through thermal degradation of kerogen but have been expelled from the source rock at an early stage of diagenesis

gc ms identification of biomarkers in road asphalts and in their parent crude oils relationships between crude oil maturity and asphalt reactivity towards weathering abstract asphalt cements vacuum residues of petroleum used as binders for road construction can undergo weathering phenomena or natural oxidation to various degrees depending on their chemical structures and on their origin the first aim of this study was to determine the characteristics of the source rocks generating the parent crude oils the second aim was to correlate the chemical structures of recovered asphalt cements to the genesis data of their parent crude oils in order to predict their sensitivity towards weathering towards these ends saturated fractions of sixteen asphalt cements and their parent crude oils have been analysed by gc ms sir many linear branched and naphthenic compounds from the saturated hydrocarbon fraction have been identified hopanes m z 191 norhopanes m z 177 163 and steranes m z 217 and 218 have been selected to characterize original and weathered asphalts as well as their parent crude oils using geochemical indices t s t s t m c29 steranes etc aliphatic structures of the asphalts and corresponding crude oils could be differentiated through principal component analysis pca the selected variables involve geochemical indices and asphalt rheological characteristics results are in good agreement with the classification obtained from ftir indices linear alkanes branched aliphatics aliphatics versus aromatic structures etc moreover good correlations in geochemical indices have been found between asphalts and their parent crude oils finally it was also possible to predict some rheological properties e g stiffness at low temperature using a multilinear regression which involves geochemical indices of parent crude oils before any physical transformation distillation etc and ftir indices of corresponding asphalt cements

middle to late cenozoic basin evolution in the western alborz mountains implications for the onset of collisional deformation in northern iran carbonates and basalt flows yielding 40 ar 39 ar ages of 32 7 0 3 and 32 9 0 2 ma the gand ab unit is correlated with the oligocene lower miocene qom formation of central iran and is considered a product of thermal subsidence following eocene extension the narijan unit unconformably overlies the gand ab unit and is composed of fluvial lacustrine and alluvial fan sediments exhibiting contractional growth strata we correlate the narijan unit with the middle to upper miocene upper red formation of central iran on the basis of lithofacies similarities stratigraphic position and an 8 74 0 15 ma microdiorite dike 40 ar 39 ar that intruded the basal strata deformation timing is constrained by crosscutting relationships and independent thermochronological data the parachan thrust system along the eastern edge of the ancestral taleghan alamut basin is cut by dikes dated at 8 74 0 15 ma to 6 68 0 07 ma 40 ar 39 ar subhorizontal gravels that unconformably overlie tightly folded and faulted narijan strata are capped by 2 86 0 83 ma 40 ar 39 ar andesitic lava flows these relationships suggest that alborz deformation had migrated southward into the taleghan alamut basin by late miocene time and shifted to its present location along the active range front by late pliocene time data presented here demonstrate that shortening in the western alborz mountains had started by late middle miocene time this estimate is consistent with recent thermochronologicalresultsthatplacetheonsetofrapid exhumation in the western alborz at 12 ma moreover nearly synchronous miocene contraction in the alborz zagros mountains turkish iranian plateau and anatolia suggests that the arabia eurasia collision affected a large region simultaneously without a systematic outward progression of mountain building away from the collision zone citation guest b b k horton g j axen j hassanzadeh and w c mcintosh 2007 middle to late cenozoic basin evolution in the western alborz mountains implications for the onset of collisional deformation in northern iran tectonics 26 tc6011 doi 10 1029 2006tc002091

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

possible origin of 25 norhopanes in jurassic organic poor mudstones from the northern qaidam basin nw china 25 norhopanes have been found for the first time in jurassic organic poor mudstones in the northern qaidam basin northwestern china the carbon number distribution in the m z 177 mass chromatograms does not consist of the full suite from c 28 to c 34 although this is a well known feature generally ascribed to 25 norhopanes in source rocks the ranges of c 29 25 norhopane c 29 30 norhopane and c 29 25 norhopane c 30 hopane are 0 07 0 08 and 0 03 0 04 respectively these values are within the recognized global background level for 25 norhopane concentrations in source rocks blanc p l connan j 1992 origin and occurrence of 25 norhopanes a statistical study organic geochemistry 18 813 828 here we provide additional evidence for the existence of 25 norhopanes in mudstones source rocks they were not detected in organic rich mudstones implying that the accumulation or diagenesis of the organic poor mudstones may have provided the right conditions for the formation of 25 norhopanes the depositional setting is suggested to be anaerobic and distant from the lacustrine lakeshore based on biomarker and petrological features and previous sedimentary environment studies in such a nutrient limited environment with relatively low source organic matter microbial reworking of biomass occurred microbial consortia scavenged the existing hopanoids contributing biomass and releasing nutrients to perform 25 norhopane forming reactions

geochemical and biological marker assessment of depositional environments using brazilian offshore oils abstract a combined geochemical and molecular characterization of a wide selection of oils from the major brazilian offshore basins has been undertaken the elemental sulphur nickel and vanadium and bulk oapi and 13c properties of each sample been considered together with its molecular composition determined using liquid and gas chromatography and quantitative biological marker investigations using gas chromatography mass spectrometry for alkanes the results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups the distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils each group is correlated tentatively with source rocks laid down in a specific depositional regime namely lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate or marine deltaic the diagnostic features that allow this classification are the relative abundance and carbon number distributions of n alkanes pristane phytane ratios sulphur nickel and vanadium contents carbon isotope data the absolute concentrations of hopanes and steranes and their abundance relative to 4 methylsteranes and also the occurrence and abundance of several specific biological markers including 18 h oleanane gammacerane carotane tricyclic terpanes higher acyclic isoprenoids 28 30 bisnorhopane and 25 28 30 trisnorhopane this investigation shows the value of a combined geochemical and molecular approach in the assessment of the palaeoenvironment of deposition of the source rocks which gave rise to the oils

the use of bisnorhopane as a stratigraphic marker in the oseberg back basin north viking graben norwegian north sea abstract this paper discusses the occurrence of 28 30 dinor 17 18 21 hopane bisnorhopane in stratigraphically fairly well preserved viking group sections from wells in local depressions in the north viking graben area the results show the presence of high relative amounts of bisnorhopane in the syn rift sections whilst the post rift sections contain little or no bisnorhopane since most exploration wells are drilled on structural highs primarily penetrating the post rift draupne this may explain why many analyzed source rock sections in this area contain little bisnorhopane as a correlation of draupne sections using the vertical relative bisnorhopane distributions it is suggested to be a potential stratigraphic marker for the area indicating the presence of syn rift draupne sediments the relative bisnorhopane amounts follow a logarithmic reduction with depth and thermal maturity the bisnorhopane signal is nearly extinguished at 3700 m depth at a maturity of r o 0 9 1 0

investigation of hydrocarbon biodegradation from a downhole profile in bohai bay basin implications for the origin of 25 norhopanes abstract a suite of reservoir cores oil sands from a single well in bohai bay basin east china displayed a progressive increase in petroleum biodegradation extent on the basis of bulk composition and 25 norhopane content this fits with the proposal that subsurface petroleum biodegradation is dominantly an anaerobic process and usually occurs at the oil water contact it is likely that sequential microbial degradation of hydrocarbons under anoxic conditions does not occur in a true stepwise fashion but is controlled by various factors such as concentration and solubility of hydrocarbons and their diffusion rate to the oil water contact in fact 25 norhopanes were formed prior to the complete elimination of the acyclic and mono and bicyclic alkanes an inverse response of the 22 s 22 s 22 r ratio between each extended 17 h hopane and its corresponding 25 norhopane was observed as severe biodegradation occurred supporting the proposal that the 25 norhopanes originate from demethylation of hopanes field observation revealed that biomarkers without extended alkyl side chains such as oleanane gammacerane and carotane have significant resistance to biodegradation and can be used as naturally occurring internal standards to evaluate variations in other biomarkers the results suggest that the quantity of 25 norhopanes showed a minor increase as the hopanes decreased significantly i e only partial hopane conversion to the corresponding 25 norhopanes alternative degradation pathways for hopanes might occur in reservoirs in addition to c 25 demethylation

origins of palaeozoic oils in the tarim basin evidence from sulfur isotopes and biomarkers abstract crude oil h 2 s and pyrite samples from palaeozoic formations in the tarim basin have been analyzed for 34 s values together with oil samples for biomarkers and fluid inclusions for chemical composition to elucidate the origin of sulfur in the oil and to address potential applications in oil source rock correlation the results show that crude oil samples have sulfur contents from 0 02 to 2 47 and 34 s values from 11 9 to 28 2 non degraded oils without associated h 2 s gas have 34 s values from 11 9 to 20 5 and are relatively rich in c 28 20r sterane aryl isoprenoids and or gammacerane the features are well correlated with the cambrian and lower ordovician source rocks with 34 s values from 10 4 to 19 4 non degraded oils with associated h 2 s gas have 34 s values from 15 1 to 19 1 close to the h 2 s from 15 0 to 18 5 suggesting that the h 2 s was incorporated into the oils leading to the generation of 2 thiaadamantanes and likely alkyl thiolanes in the oil with a 34 s value of 18 5 heavily biodegraded oils have the highest sulfur contents and show 34 s values from 20 0 to 28 2 significantly heavier than those of any of the potential source rocks 15 3 to 19 4 thus it is likely that isotopically heavy sulfides have been incorporated into the biodegraded oils resulting in 34 s values of the oils becoming closer to cambrian and ordovician age seawater sulfates the sulfides may have originated from thermochemical sulfate reduction tsr as evidenced by the occurrence of h 2 s rich fluid inclusions and late stage and fracture filling pyrite with 34 s values mainly from 25 to 34 in the palaeozoic reservoirs

reworked triterpenoid and steroid hydrocarbons in a recent sediment abstract the distributions of steranes pentacyclic triterpanes and aromatic steroid hydrocarbons in core sections of a recent intertidal sediment bridgwater bay severn estuary u k have been examined by gas chromatography mass spectrometry depending on sample depth the distributions are explicable in terms of 1 i a reworked origin for these compounds from a geological source probably as a result of erosion of nearby organic rich sediments of lower liassic age or 2 ii a dual origin from both i and a more mature source probably an anthropogenic input of petroleum origin these results show that not all of these steroid and triterpenoid hydrocarbons in surface sediments necessarily result from fossil fuel pollution they indicate also that attention should be paid to the possibility of contributions from reworked components when using the distributions of these compounds in geochemical studies of sediments that are low in extractable organic matter

25 norhopanes formation during biodegradation of petroleum in the subsurface abstract quantitative data from petroleum systems in china liaohe basin and canada athabasca tar sands support the theory that 25 norhopanes are produced during biodegradation of petroleum in the subsurface within a single oil column both case histories showed increasing severity of degradation indicated by destruction of hopanes and production of 25 norhopanes downward to the oil water contact in the athabasca samples between the peters k e moldowan j m 1993 the biomarker guide interpreting molecular fossils in petroleum and ancient sediments prentice hall englewood cliffs new jersey p 363 scale of biodegradation levels 5 9 concentrations of c 28 20s triaromatic steroids and other biodegradation resistant compounds increased by 35 reflecting a concentration effect as a consequence of removal of more degradable compounds over the same interval the concentrations of c 28 17 25 norhopane and c 29 17 25 norhopane increased by an order of magnitude thus requiring that the balance be met by their net production during degradation a detailed molecular investigation of the athabasca bitumen revealed that c 30 17 hopane degrades faster than c 29 17 hopane whilst the rate of formation of both c 29 17 25 norhopane and c 28 17 25 norhopane are similar complicating a straightforward interpretation of demethylation of hopanes to form 25 norhopanes hopane degradation in the athabasca tar sand may also occur without the production of 25 norhopanes the results show that even within a single petroleum accumulation a number of mechanisms control changes in the abundance and composition of hopanes and 25 norhopanes

nature and origins of internal sediments in jurassic limestones of burgundy franc and fnoud algeria numerous hard grounds and palaeo emersion surfaces in middle jurassic grainstones of burgundy france and upper jurassic micritic limestones of the fnoud region algeria exhibit a variety of diagenetic cements and internal sediments four types of internal sediments have been defined each being the product of a particular environment type 1 unsorted microbioclastic wackestone characterizes submarine hard grounds type 2 pelleted grainstone with inverse graded bedding occurs in microcaverns developed in palaeobeach rocks type 3 centrifugal micrite seems to characterize relatively dry supratidal substrates type 4 crystal silt is associated with early sparitic cements and dissolution phenomena indicating the influence of non marine waters within a given pore space a centripetal succession of various cements and internal sediments seems to reflect the lateral evolution of the tidal flat or beach at any given pore space interstitial waters have evolved progressively as the intertidal zone advanced or receded thus internal sediments and related early diagenetic phenomena are valid criteria both for particular environments and for the general evolution of the coastal plain finally although internal sediments may accumulate both within grainstones burgundy and mudstone substrates fnoud these textural differences may influence the type and frequency of internal sedimentation resume de multiples ciments diagenetiques et sediments internes precoces ont ete reconnus dans les nombreuses surfaces durcies et surfaces d emersion des calcaires grainstones du jurassique moyen de bourgogne france et des calcaires micritiques de la region des fnoud algerie quatre types principaux de sediments internes ont ete definis chacun etant le produit d un milieu diagenetique particulier le type 1 est un wackestone rnicrobioclastique non classe qui caracterise les surfaces durcies sousmarines le type 2 est un micrograinstone a pellets avec granoclassement inverse qui existe dans les microcavernes developpees dans les paleo gres de plage le type 3 est une micrite centrifuge qui se developpe dans des conditions supratidales le type 4 consiste en un silt a debris de cristaux associe aux ciments sparitiques precoces et aux phenomenes de dissolution caracterisant ainsi l influence d eaux non marines dans un pore donne la succession centripete entre ciment et sediments internes reflete i evolution laterale de la plaine cotiere ou de la plage suivant le regime sedimentaire dans cet espace poreux les eaux intersticielles evoluent progressivement au fur et a mesure que la zone intertidale s accro t ou se reduit ainsi les sediments internes et les phenomenes diagenetiques associes constituent de bons criteres pour la determination d un environnement particulier et pour retracer i evolution generale de la plaine cotiere enfin bien que les sediments internes se deposent au sein de calcaires grainstones bougogne ou de calcaires mudstones fnoud les differences texturales du sediment hote peuvent influencer sur le type et la frequence de la sedimentation interne

paleoecological constraints on reef coral morphologies in the tortonian early messinian of the lorca basin se spain abstract coral reefs represent one of the main carbonate factories that contributed to the control of the stratigraphic architecture of carbonate platforms which had a widespread development during the late miocene in the paleo mediterranean area the late miocene reef complexes of the lorca basin in southeastern spain are composed of five mixed siliciclastic carbonate units middle tortonian to early messinian in age the development of coral reefs probably ceased when the first evaporitic event occurred in the basin centre in the early messinian this study mainly focuses on the response of reef communities and the modifications of reef organisation to global and regional parameters at the platform scale the carbonates are intermixed with terrigenous deposits related to two main types of clastic systems torrential fans and fluvial to deltaic systems the amount of clastic input greatly affected reef growth and coral morphologies three different types of stratal geometries were delineated in the reef complex sigmoids bioherms and patches and carpets the reef frameworks are mainly constructed by a poorly diversified assemblage of corals composed of poritids faviids and mussids porites is the principal reef builder of the sigmoids and carpets where it is widely distributed tarbellastraea is common in bioherms and acanthrastraea appears generally associated with porites in patches five basic growth forms of porites are observed thin branching or finger shaped thick branching to columnar domed to hemispheric encrusting and platy to dish differences in coral morphology are used to define a relative water depth zonation in monogeneric reefs the distribution of these growth forms was principally controlled by water depth the reef flat is dominated by small thin branching or finger shaped corals that are replaced towards the reef front by domed to hemispheric corals commonly encrusted by coralline algae downslope columnar morphologies grade into thin branching shapes the reef morphologies are variable throughout the five mixed siliciclastic carbonate units at the platform scale the first and oldest unit is dominated by bioclasts whereas units 2 3 and 5 are porites dominated sigmoid complexes unit 4 is a well developed biohermal complex mainly composed of tarbellastraea these units started to develop as early as middle tortonian and stopped as late as early messinian and show a progradational trend where the two latest units are well developed thus carbonate production changed from grain producing biota in the basal unit to framework producing biota in the overlying units consistent with evolution from a distally steepened ramp to a reef rimmed shelf at the scale of individual reef units the relative water depth zonation of the corals is controlled by ecological changes substrate nutrients synecologic relations and diversification of coral species in the transects across the carbonate platform related to the different units the coral zonation records changes in spatial distribution of corals in response to ecological stresses and changes in regional and global environments tectonic relative sea level changes and runoff

building the zagros collisional orogen timing strain distribution and the dynamics of arabia eurasia plate convergence he zagros mountains are the result of the arabia eurasia collision initiated at 35 ma as the rifted arabian lithosphere was underthrusted beneath the iranian plate due to its negative buoyancy the onset of crustal thickening started at 25 ma as recorded by the hinterland exhumation and foreland clastic deposition deformation throughout the arabia eurasia collision zone and the uplift of the iranian plateau occurred after 15 12 ma as a result of shortening thickening of the thin iranian crust we emphasize that only 42 of the post 35 ma convergence is partitioned by shortening within central iran tomographic constraints show ongoing slab steepening or breakoff in the nw zagros whereas underthrusting of the arabian plate is observed beneath central zagros the current subduction dynamics can be explained by the original lateral difference in the buoyancy of the distal margin that promoted slab sinking in nw zagros and underthrusting in central zagros critical wedge approach applied to the zagros favors the hypothesis of strong brittle crust detached above a viscous lower crust in contrast the weak sedimentary cover deforms by buckling of a thick multilayered cover thrust faulting associated with folding occurs in the competent layers and is responsible for most of the earthquakes there is evidence that the role of the slab pull force in driving the arabian plate motion was reduced after 12 ma large scale mantle flow induced by mantle upwelling at the afar plume appears to be the main driver of the arabia plate motion we stress that the main kinematic change in the zagros region occurred at 15 12 ma as the zagros uplifted before the arabian slab detached the zagros appears key to investigate coupling between continental rheology plate driving forces and mountain building in which the role of rift inheritance appears to be central

organofacies variation control on hydrocarbon generation a lower congo coastal basin angola case history abstract a group of lower congo coastal basin angola carbonate platform petroleums all determined to be of lower cretaceous pre salt bucomazi fm neocomian aptian rift phase provenance showed considerable internal diversity recognised in terms of biomarker abundances and waxiness this variation was particularly evident in their carbon isotopic compositions which ranged from 26 4 to 29 7 ppt although not exclusive to all oils many contained an abundance of an unusual triterpane tentatively characterised as 25 30 bisnorhopane using a combination of kerogen type i ii iii and kinetic data ea and a plus kerogen pyrolysate isotopic signatures a conspicuous variation in organofacies was observed over the vertical and lateral development of this lacustrine source unit in a series of control wells three oil prone organofacies were recognised two of which could be individually characterised as type i 13c depleted and type ii 13 c enriched assemblages a third assemblage of type ii iisuperior character and intermediate isotopic signature not dependent upon mixing of the above end members was similarly recognised significantly the 25 30 bisnorhopane marker observed in many of the oils was found to be exclusively associated with the type ii 13c enriched organofacies on this basis rationalisation of crrde oil character and genera was possible in terms of phased co generation from these limiting organofacies with subsequent co mingling of the resultant oils although dissimilar end member oils could be isotopically matched to source facies representative of the more labile type ii lower ea to the less labile type i higher ea candidates most oils showed a mixed character reflecting their aggregate compostion definition of organofacies make up and variation is crucial to the fine tuning of contemporary modelling practises in their application to the study of hydrocarbon productive habitats

organic geochemistry of venezuelan extra heavy crude oils 2 molecular assessment of biodegradation abstract the extent of biodegradation of extra heavy crude oils from the eastern venezuelan basin orinoco tar belt has been assessed using biological marker compounds which include steranes triterpanes aromatic steroids and phenanthrenes analyzed by gc ms and petroporphrins analyzed by hplc the analyses indicate that biodegradation takes place in two regions namely surface or close to surface and subsurface with a different pattern of biodegradation taking place at each type of location some oils show patterns of biomarkers which may be the combined result of degradation at both main sites of biodegradation however two empirical biodegradation parameters are proposed to achieve this classification the classification of crude oils in terms of degree of biodegradation is further complicated by the identification of mixed crudes

environmental factors influencing skeletal grain sediment associations a critical review of miocene examples from the western mediterranean the presence of foramol rhodalgal and bryomol skeletal grain associations in ancient shallow marine limestones is commonly interpreted as evidence for non tropical palaeoclimate despite temperature being only one of several factors influencing skeletal grain associations such interpretations neglect the multitude of factors other than temperature that influence carbonate producing biota these include nutrients water energy water transparency depth of the sea floor salinity oxygen ca2 and co2 concentrations mg ca ratio alkalinity substrate requirements competitive displacement as well as biological and evolutionary trends this uniformitarian approach also disregards the probability that conditions of present day biological systems may not be representative of past conditions of analogous systems here the importance of considering these other factors is illustrated through two examples of carbonate platforms in the western mediterranean these platforms are dominated by foramol rhodalgal and bryomol associations of miocene age in spite of having formed in tropical conditions the platforms discussed are 1 the lower tortonian ramp on menorca balearic islands and 2 the lower middle miocene ramps of the central apennines italy evidence for tropical conditions in the mediterranean during the period of growth of these platforms is provided by species of red algae and larger foraminifera by data from coeval continental basins and by global oxygen isotope data

comparisons of the kinematics and deep structures of the zagros and himalaya and of the iranian and tibetan plateaus and geodynamic implications 1 we compare the geologic histories the deep structures and the present day kinematics of deformation of the himalaya and the adjacent tibetan plateau with those of the zagros and iranian plateau to test geodynamic processes of continental collision shortly after india and arabia collided with eurasia horizontal shortening manifested itself by folding and thrust faulting of sedimentary rock detached from india s and arabia s underlying crystalline basement subsequently slip on thrust faults stacked slices of india s basement to build the himalaya on india s northern margin such faulting has not yet developed in the zagros where collision is more recent and arabia penetrates into eurasia more slowly than india does so that postcollision convergence with eurasia is less the greater elevation thicker crust and more marked heterogeneity of the upper mantle beneath the tibetan than beneath the iranian plateau also reflect a more advanced stage of development moreover while thrust or reverse faulting and crustal shortening continue on the margins of both plateaus normal faulting suggesting horizontal extension and crustal thinning occurs within tibet but not in iran hence the balance of forces that built the high tibetan plateau must have changed apparently some time since 15 ma removal of tibetan mantle lithosphere could have altered that balance if mantle lithosphere beneath the iranian plateau has been removed however the change in force balance has been too small to initiate normal faulting low seismic wave speeds in the uppermost mantle just beneath the moho of both plateaus suggest to us that lithosphere beneath both is thin consistent with late cenozoic removal of it but alternative explanations might account for these low speeds despite its apparently thin and hence presumably weak mantle lithosphere much of central iran undergoes little deformation it illustrates how a crustal block can behave rigidly not necessarily because it is strong but because deviatoric stresses can be small whereas differences between the two regions clearly depend on the amount that arabia and india have penetrated into eurasia which scales with both the dates of collision and rates of convergence we see no differences in the operative processes that depend on the present day rates of convergence

the occurrence of bisnorhopane trisnorhopane and 25 norhopanes as free hydrocarbons in some australian shales abstract the triterpenoid hydrocarbons of some west australian shales have been examined by gc ms in addition to the common 17 h 21 h hopanes 17 h 21 h hopanes and 17 h 21 h moretanes 28 30 bisnorhopane 25 28 30 trisnorhopane and 25 norhopanes were identified in the organic extracts in contrast pyrolysates of the solvent extracted sediments contained only the common hopane and moretane series indicating that 28 30 bisnorhopane 25 28 30 trisnorhopane and 25 norhopanes are not bonded to kerogen but rather are present in the sediments as free hydrocarbons

mineralogical and geochemical evidence for biogenic and petroleum related uranium mineralization in the qianjiadian deposit ne china abstract the sandstone hosted qianjiadian uranium deposit hosted in the upper cretaceous yaojia formation in the qianjiadian area songliao basin ne china has been studied for over twenty years however there exists debate on whether mineralization fluid is low temperature groundwater in favor of biogenic mineralization or diabase related magmatic hydrothermal fluid for this deposit and other adjacent geologically linked sandstone hosted uranium deposits baixingtu baolongshan and huitianzhao deposits in the north china this study provided new data from petrographic and geochemical analyses geochronology of uranium minerals the empa chemical dating method and petroleum hydrocarbon biomarkers in host sandstones two types of host sandstone were recognized in calcareous sandstones pitchblende coexists with colloform pyrite and poikilitic calcite cement while quartz and feldspars were extensively corroded in non calcareous sandstones coffinite coexists with colloform pyrite and only feldspars were slightly corroded this suggests that pitchblende formed in high ph ph 9 fluid while the ph of ore forming fluid for coffinite was lower ph 7 9 besides empa chemical dating revealed two stages of uranium mineralization stage a occurred in 43 28 ma with pitchblende as the only uranium mineral species stage b occurred in 19 3 ma with the formation of both pitchblende and coffinite the uranium mineralization was biogenic under low temperature groundwater condition and thus not from a diabase related mafic magmatic hydrothermal fluid based on the following lines of evidence i some coffinite occurs as phosphorus rich microorganism like microspherules structure ii pyrite aggregates were generated from bacterial sulfate reduction as indicated by the 34s values as low as 41 4 iii calcite cement in calcareous sandstone contains only single phase aqueous inclusions and have 13c values as low as 11 2 indicating that part of the carbon was derived from organic matter oxidation iv the organic matter oxidation is further supported by hydrocarbons extracted from petroleum inclusions within calcite cement showing occurrence of c26 c31 17 21 25 norhopanes typically resulting from heavy biodegradation

fluid inclusion evidence for an early marine sourced oil charge prior to gas condensate migration bayu 1 timor sea australia the distribution of oil bearing fluid inclusions fi in currently gas bearing jurassic reservoir sandstones from bayu 1 northern bonaparte basin timor sea is consistent with the bayu gas condensate field originally containing a palaeo oil column beneath a thick palaeo gas cap in order to assess the origin of the oil trapped in the fis and its relationship if any to the gas condensate a detailed molecular geochemical study was carried out on a fi oil extract and a condensate sample recovered from a similar interval by modular formation dynamics tester mdt compared to the condensate the fi oil was generated from a more marine influenced less clay rich source rock or source facies which was deposited in a less oxic environment with greater eukaryotic input the source rock of the condensate was more terrigenous and had greater microbial input the bayu fi oil contains a greater amount of c28 and c29 tricyclic terpanes than the bayu condensate and particularly compared to the elang plover sourced oils from further to the northwest e g corallina and laminaria which are more terrestrially dominated the bayu condensate has previously been attributed to either the marine cretaceous echuca shoals formation or mixed sourcing from the less terrestrially influenced facies of the jurassic elang and plover formations together with the marine flamingo group analysis of the fi oil confirms a more marine influenced source facies of the palaeo oil with the echuca shoals formation being the most likely source based on oil oil and oil source correlations the fi oil appears to represent a marine source end member and it is likely that mixing of this oil sourced from the echuca shoals formation with hydrocarbons sourced from the more terrestrially dominated plover elang source facies could account for the intermediate composition of the currently reservoired condensate a discrete flamingo group is not required and this oil family may not be present in the bayu area the differences are nevertheless subtle and a contribution from the flamingo group cannot be completely discounted the fi oil has a mid oil window maturity 0 75 vitrinite reflectance equivalent vre whereas the currently reservoired condensate has a higher maturity 0 9 vre these maturity data are consistent with early expulsion from the more labile marine derived organic matter in the echuca shoals formation followed by expulsion of large amounts of condensate from the more terrestrially dominated elang and plover formations three possible transition mechanisms from gas over oil to condensate are consistent with the fi petrographical and geochemical data the first charge may have 1 been lost by breaching of the seal 2 been displaced by the condensate or 3 been partly dissolved in the later condensate charge a combination of factors 2 and 3 is considered most likely but further investigation is required to assess these options the fi oil at bayu 1 predominantly represents a different hydrocarbon charge compared to the condensate liquid and so by analogy the large residual oil columns that are observed elsewhere in the northern bonaparte basin are unlikely to be due to water washing of a pre existing gas condensate column similar to bayu undan

identification and geochemical significance of demethylated highly cyclized regular polyprenoids in oils and source rocks abstract polycyclic polyprenoid hydrocarbons and related demethylated compounds have been identified in severely altered bitumen from oil stained rocks of upper jurassic lower cretaceous age they occur as three series one homologue of which has been isolated and structurally characterized from nuclear magnetic resonance nmr studies they comprise hydrocarbons demethylated at the a b ring junction compounds demethylated at rings e f g and a novel series of compounds demethylated at both the ring a b junction and the ring e f g junction identified for the first time the occurrence in a number of unaltered and biodegraded oils and source rocks of upper jurassic lower cretaceous age of non demethylated hydrocarbons together with related series demethylated at rings e f g indicates that the demethylation process is unlikely to be related to a late degradation process but rather results from the early transformation of precursors bearing functionalised methyl groups on rings e f g in contrast polycyclic polyprenoid hydrocarbons demethylated at the a b ring junction occur only in the most biodegraded samples suggesting that this demethylated series is formed at later stages of alteration by further demethylation of both non demethylated compounds and compounds demethylated at rings e f g in addition a novel series of carboxylic acids related to the polycyclic polyprenoids has been tentatively identified using gas chromatography mass spectrometry gc ms and comprises both non demethylated and demethylated structures at rings e f g it is proposed that the acids represent alteration products of polyprenoids bound to aromatic sub units from macromolecular material that have been released upon severe oxidation during exposure to biodegradation weathering

late cretaceous anoxic events in the brazilian continental margin abstract a combined geochemical and micropalaeontological study of cenomanian to maastrichtian pelitic sediments from the brazilian continental margin has been undertaken the organic carbon contents rock eval pyrolysis results and biological marker distributions together with the taxonomic selection and distribution patterns of microfossil assemblages indicate that intermittent anoxic events occurred in the brazilian marginal basins during the cenomanian santonian with deposition taking place in progressively deeper waters from neritic to bathyal such events are characterised by the following 1 i a predominance among the benthonic foraminifera of low diversity small sized specimens mainly composed of gavelinellids buliminids and nodosariids indicating dysaerobic bottom conditions 2 ii levels with virtually no benthonic foraminifera and a well developed planktonic biota foraminifera radiolarians and diatoms indicating anaerobic bottom conditions with oxygenated surface waters 3 iii the occurrence of organic rich calcareous mudstone sediments 4 iv features in the biological marker distributions such as high concentrations of 28 30 bisnorhopane and 25 28 30 trisnorhopane up to 130 ppm a predominance of phytane over pristane and medium to high concentrations of nickel and vanadyl porphyrins up to ca 5700 ppm the widely recognized cenomanian turonian and santonian oceanic anoxic events schlanger and jenkyns 1976 ryan and cita 1977 and jenkyns 1980 are therefore manifest in the cassipore ceara sergipe alagoas and campos basins within the brazilian continental margin as is the presence of such events in the coniacian in contrast the campanian maastrichtian appears to be a time interval when deposition under oxygenated conditions produced sediments with low organic carbon contents and poor hydrocarbon source potential containing highly diversified and abundant calcareous and agglutinated benthonic foraminifera

chemical molecular and isotopic differentiation of organic facies in the tertiary lacustrine duaringa oil shale deposit queensland australia abstract total organic matter extractable organic matter bitumen and pyrolysates released on low temperature sealed tube pyrolysis of kerogen were analysed chemically and isotopically based on bulk bitumen and biomarker parameters the sediments are immature to a depth of approx 1300 m within the terrestrial and lacustrine depositional environments of the tertiary duaringa basin various organic facies have been classified according to inorganic input and maceral abundances of organic matter derived from land plant and algal sources the latter derived mainly from pediastrum and with a varying botryococcus content the lacustrine upper lamosite is chemically and isotopically distinct from the lower lamosite due to a changing algal community relative contributions from allochthonous land plants and for the lower lamosite a slightly more saline and restricted lake environment the lower lamosite is associated with the highest concentrations of c 28 c 30 4 methylsteranes and 13 c depletion in toc in the upper lamosite there is a strong positive correlation between botryococcus content and 13 c enrichment the organically lean claystones have sources nearly identical to the lamosites but the organic matter is diluted due to rapid influx of siliciclastics the terrestrial facies the cannel coal and carbonaceous shales are mainly distinguished from the lacustrine facies by higher relative proportions of c 29 steranes c 30 4 methylsteranes and 13 c values for the pyrolysed hydrocarbons intermediate between the two lamosite facies the carbonaceous oil shale has a composite geochemical signature intermediate between the two end members lamosite and cannel coal oleanane and ring a degraded triterpanes derived from lupane arborane and oleanane skeletons are distributed throughout all organic facies representing both autochthonous and allochthonous higher plant inputs higher concentrations of oleanane and des a lupane are associated with the terrestrial facies hopanes dominate over steranes in all organic facies and their concentration ranges are independent of facies for the lamosites the aliphatic biopolymer algaenan is implicated as the dominant source for n alkanes from analysis of their yields homologue abundances and individual 13 c values in the terrestrial facies resinites are paraffinic and are a major source for the n alkanes released on pyrolysis compound specific analysis of extractable and pyrolysate hydrocarbons allowed deconvolution of different source inputs to free lipids and kerogen for the lamosites low molecular weight n alkanes in the bitumen are derived mainly from a pediastrum source while botryococcus is associated with waxy n alkanes however the situation is reversed in the kerogen pediastrum algeanan has a longer average alkyl chain length than botryococcus algaenan the magnitude of the isotopic differences between single n alkanes released at different temperatures is useful in determining multiplicity of sources