alkylbiphenyls in ancient sediments and petroleums abstract c 1 and c 2 alkylbiphenyls have been analysed in crude oils and sediment extracts by capillary gas chromatography after preliminary isolation procedures involving tlc and hplc the abundance of 2 methylbiphenyl relative to 3 methylbiphenyl has been measured in samples from two sedimentary sequences 2 methylbiphenyl decreases in relative abundance with increasing thermal maturity of the sediments in both sedimentary sequences these isomeric methylbiphenyls are potentially useful as thermal maturity indicators for crude oils

dating reservoir filling a case history from the north sea abstract secondary petroleum inclusions in reservoir sandstones in the froy field and the rind discovery are used in combination with burial history modelling reservoir oils and core extracts to shed light on how and when these structures received their hydrocarbon charges analysis of normal alkane and biomarker distributions in these three data sets fluid inclusions core extracts and drill stem tests dsts provide information on the changes in organic facies and maturity of petroleum in the various reservoir strata over time the geochemistry of core extracts and dst oils in rind and froy reveal that the maturity of the rind petroleum system is higher and also of slightly less anoxic facies compared to the oil present in the froy system biodegraded oil is found today in a small sub compartment of the froy field using the burial history of the froy and the assumption that biodegradation effectively comes to a halt at 70 80 c we tentatively conclude that the filling of this sub compartment and the biodegradation of the oil must have occurred earlier than 30 40 m y b p and before oil from the upper jurassic draupne shales more recently homogeneously filled the main froy structure at 30 40 m y b p the froy structure was at a depth of 1 5 2 km compared to the present depth of 3 5 4 km and it is more than likely that neither the heather nor the draupne formations were mature in the paleo drainage area of the field at this time still the stratigraphically deeper dunlin formation could have been mature and the geochemical signatures of the now biodegraded oil correlates with known signatures from the dunlin formation in this region in the rind discovery no fluorescent petroleum inclusions are observed in k feldspar overgrowths however the number of inclusions in quartz and plagioclase is larger than that observed in the shallower froy field from the mean homogenization temperatures of the petroleum inclusions which are close to the present reservoir temperature filling of the froy field and main rind structure is suggested to have been a recent event a presently dry compartment penetrated by well 25 2 15r2 in the rind discovery contains high residual oil saturations indicating loss of oil from this structure either by direct cap rock leakage or displacement of oil by gas and subsequent cap rock leakage numerous petroleum and coexisting water inclusions were found in the presently dry overpressured structure and it is clear from measurements of homogenization temperatures that the water and the petroleum inclusions are not both saturated with respect to gas due to the lower solubility of hydrocarbon gas in water compared to in oil it is more likely that water inclusions are closer to saturation than are the petroleum inclusions using the difference in homogenization temperatures in these two systems and the burial history we tentatively suggest that the cap rock leakage occurred later than 10 m y b p such information on time for reservoir filling and seal failure when used to calibrate basin modelling should facilitate better models for understanding movement of hydrocarbon fluids in basins

hydrocarbon composition of authigenic inclusions application to elucidation of petroleum reservoir filling history abstract geochemical analysis of petroleum inclusions trapped in authigenic feldspar and quartz in the ula formation in the north sea ula oil field revealed a petroleum of markedly different composition than the oil presently in the reservoir using microthermometry and the burial history as a dating tools it is concluded that the petroleum in the k feldspar inclusions was present in the more porous and permeable parts of the ula formation as early as 45 75 my bp when the field was at a depth of about 1 0 1 5 km as compared with the current depth of 3 4 km this early petroleum which was trapped as inclusions in authigenic k feldspar shows a distinctly different distribution of tricyclic terpanes and pentacyclic triterpanes from that of the current petroleum charge in the ula formation which was derived from the mandal formation source rock in late neogene time molecular parameters show that the oil in the k feldspar inclusions is significantly less mature than the crude oil in the present reservoir the approximate 90 c temperature increase occurring after entrapment of the early petroleum in kfeldspar the field is currently at 143 c appears not to have reset the low maturity signature of the oil in the k feldspar inclusions this could suggest that the temperature in the inclusions is too low for isomerization selective thermal degradation to occur lack of catalysts or that there are other controls on the ratio of some of these parameters still parameters like the ratio of c21 to c28 triaromatic steroids and those based on dimethyl and trimethyl naphthalenes are comparatively similar in both the inclusions and in the reservoir crude the oil inclusions in authigenic quartz and albite formed from about 10 my bp burial depth 2 5 km until the present burial depth 3 4 km are interpreted as representing a palaeo petroleum charge having a composition intermediate between the oil found in k feldspar inclusions and the oil charge in the present reservoir our data suggest strongly that the petroleum trapped in the inclusions in quartz and plagioclase represents progressive dilution of the early reservoired oil now found only in k feldspar inclusions with oil from the mandal formation analysis of solution gas in these inclusions suggests that the first petroleum associated gas to arrive at the trap from the progressively maturing mandal formation had a much wetter composition than the current reservoir solution gas to explain the present comparatively drier and isotopically lighter reservoir solution gas composition the inference is made that there has been a recent during formation of k feldspar inclusions 45 75 my bp maturation of the upper jurassic mandal formation the main source rock in this region was limited possibly to the graben axis this suggests that the petroleum found in the k feldspar inclusions was most likely derived from a deeper post caledonian palaeozoic formation

brunei darussalam characteristics of selected petroleums and source rocks abstract the development of three tertiary deltaic complexes has resulted in the deposition of up to 10 km of sandstones and shales comprising the sources and reservoirs for crude oils that occur onshore near offshore and with future exploration efforts those likely to be encountered in deepwater reservoirs north of the brunei coastline we examined a series of offshore oils and onshore rock samples in brunei darussalam a to delineate oil family groups and their source rock characteristics and b to assess the source potential of the sedimentary sequence with respect to lithology and depositional setting twelve offshore oils and 53 shales coaly shales and coals were examined the oils contain indicators of allochthonous e g bicadinanes oleananes and autochthonous e g cholestanes and methylcholestanes components in the source organic matter predictable geographic variations of this mixed input are clearly evident in the sample set e g allochthonous input appears to increase in offshore brunei to the northeast although this molecular source signature is relatively clear migration of these oils from deep and unidentified source rocks has resulted in extensive migration contamination with respect to the tetracyclic and pentacyclic hydrocarbons this contamination has resulted in strong correlations between certain molecular maturity indicators and the present day temperature of the reservoirs liquid hydrocarbon source rock potential is present in the tidal and coastal embayment facies and is greatest in the miocene coals neither the shales nor coaly shales contain significant oil generative potential the thermal immaturity of the sample set precludes valid oil source rock correlations without conducting artificial maturation experiments on the coals

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

geochemical character and origin of oils in ordovician reservoir rock illinois and indiana usa twenty three oils produced from reservoirs within the ordovician galena group trenton equivalent and one oil from the mississippian ste genevieve limestone in the illinois and indiana portions of the illinois basin are characterized two end member oil groups 1 and 2 and one intermediate group 1a are identified using conventional carbon isotopic analysis of whole and fractionated oils gas chromatography gc of saturated hydrocarbon fractions isotope ratio monitoring gas chromatography mass spectrometry irm gc ms of n alkanes ranging from c15 to c25 and gas chromatography mass spectrometry gc ms of the aromatic hydrocarbon fractions group 1 is characterized by high odd carbon predominance in mid chain n alkanes c15 c19 low abundance of c20 n alkanes and an absence of pristane and phytane group 1a is characterized by slightly lower odd carbon predominance of mid chain n alkanes greater abundance of c20 n alkanes compared to group 1 and no pristane and phytane the carbon isotopic composition of n alkanes and the distribution of n alkylarenes for groups 1 and 1a indicate that these oils were generated from strata containing abundant gloeocapsomorpha prisca in contrast group 2 is characterized by low odd carbon predominance in mid chain n alkanes moderate abundance of c20 n alkanes and the presence of pristane and phytane the mississippia reservoired oil is characterized by low odd carbon predominance in mid chain n alkanes and greater abundances of c20 n alkanes pristane and phytane compared to group 2 distributions of isoprenoidal alkylarenes aryl isoprenoids for group 2 and the mississippian reservoired oil are similar suggesting that aryl isoprenoids fail to provide a diagnostic characteristic that can be used to precisely correlate oils and source rocks conventional correlations of oil to source rock based on carbon isotopic type curves and hopane m z 191 and sterane m z 217 distributions are of limited use in distinguishing ordovician reservoired oil groups and determining their origin oil to source rock correlations using the distribution and carbon isotopic composition of n alkanes and the m z 133 chromatograms of n alkylarenes show that groups 1 and 1a originated from strata of the upper ordovician galena group group 2 either originated solely from the upper ordovician maquoketa group or from a mixture of oils generated from the maquoketa group and the galena group the mississippian reservoired oil most likely originated from the devonian new albany group the use of gc irm gc ms and gc ms illustrates the value of integr ted molecular and isotopic approaches for correlating oil groups with source rocks

methylhopanoids molecular indicators of ancient bacteria and a petroleum correlation tool abstract methylhopanoids are organic compounds synthesized by certain bacteria that when preserved in sediments act as molecular fossils or biomarkers for organic matter inputs from specific bacterial sources two series of methylhopanoids occur each mainly deriving from a distinct bacterial source cyanobacteria 2 methyl and methanotrophic bacteria 3 methyl the abundance and composition of methylhopanoids within sediments of modern depositional environments varies widely apparently due to different bacterial communities contributing to the sedimentary organic matter comparable molecular characteristics are found in oils and their source rocks consequently methylhopanoids are valuable in oil oil and oil source rock correlations distinguishing between samples related to different depositional environments in particular abundant 3 methylhopanoids from methanotrophic bacteria or an additional unknown bacterial source are characteristic of some modern alkaline saline lake environments comparable compositional features in the methylhopanes of oils allow the assignment of lacustrine oils offshore west africa to two distinct lacustrine source rock facies and to distinguish between different marine source facies thus refining oil source rock correlation

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

structure of the papuan fold belt papua new guinea 1 the structure of the papuan fold belt differs substantially from the classical thin skinned structures of the canadian rockies mainly due to the weak and broken papuan lithosphere and incompetent clastic section compared to the strong cratonic lithosphere in canada overlain by limestones and quartzites the papuan margin was dissected by mesozoic extensional faults in part reactivated during neogene compression which created basement involved anticlines or elevated plateaus in the papuan fold belt the sedimentary section in the fold belt is deformed into large ramp anticlines in the southwest smaller miocene and mesozoic duplexes in the center and fault propagation folds in the northeast hydrocarbon discoveries to date have occurred in the southwestern anticlines which are interpreted as reactivated extensional structures the precursor rollover anticlines trapped oil generated in the late cretaceous such that present accumulations probably result from preservation of that oil during neogene thrusting mesozoic duplex structures are likely to be prospective but difficult to define and fault propagation folds rely upon unproven upper cretaceous sandstones as a reservoir

the australasian tektite source crater found at last in pnas sieh et al 1 present the best candidate yet for the long sought source crater of the australasian tektite strewn field unlike the other 4 or so tektite strewn fields each of which can be traced back to a large impact crater the australasian field s source has yet to be definitively located while this proposal does not fully prove the case it offers strong evidence implicating a 15 km diameter impact crater in laos that has been hiding in plain sight beneath a mass of younger volcanic rocks from here it is clear that the next step in proving its parentage must be drilling through the volcanic rocks into the putative impact rocks below tektites are centimeter scale black or green blobs of glass that have long fascinated humans 2 moldavites an eastern european variety were found interred with the much more famous venus of willendorf dating back to 30 000 bce possibly reflecting our ancestors interest in unusual rocks as well as female deities individual tektites occur in widely strewn fields of which about 4 are currently known there are other candidate strewn fields each of these fields which extend over hundreds to thousands of kilometers is associated with a meteorite impact crater except one the biggest of them all the australasian strewn field it ranges south from southeast asia across australia then south of tasmania to east antarctica with a western extension that crosses over madagascar and an eastern extension into the western pacific ocean covering about 10 of earth s surface the tektites in this enormous field have been intensively studied using modern analytical methods they are divided into a number of distinct types ranging from meter scale irregular masses of black glass called muong nong 1 1email jmelosh at purdue edu 1 xref corresp 1 1

assessing the maturity of oil trapped in fluid inclusions using molecular geochemistry data and visually determined fluorescence colours abstract the thermal maturity of oils extracted from inclusions and the fluorescence colours of oil bearing fluid inclusions have been measured in 36 sandstone samples from australasian oil fields the inclusion oils were analysed using an off line crushing technique followed by gc ms a maturity assessment was made for each inclusion oil using 25 molecular maturity ratios including a newly defined dimethyldibenzothiophene ratio dmdr each inclusion oil was placed in one of 4 maturity brackets approximately equivalent to early mid peak and post oil generation windows the fluorescence colours of oil inclusions were visually discriminated into blue white and yellow plus orange and their proportions estimated using point counting techniques sixteen samples have 85 of oil inclusions with blue fluorescence whilst other samples have more variable fluorescence colours one sample has 100 of oil inclusions with yellow plus orange fluorescence the results show that samples containing mainly blue fluorescing oil inclusions have thermal maturities anywhere within the oil window in particular the molecular geochemical data strongly suggests that oil inclusions with blue fluorescence can have relatively low maturities calculated reflectance

layered tektites a multiple impact origin for the australasian tektites abstract high precision neutron activation studies of southeast asian tektites confirm their close compositional relationship to well mixed continental sediments in confirmation of earlier studies concentrations of the volatile metals zn ga as and sb are 2 4 times lower in splash form tektites than in layered or muong nong type tektites the th u ratio is higher in splash form than in layered tektites this implies loss of about 30 of the initially present u from the splash form tektites volatile contents of layered tektites are similar to those in continental sediments indicating minor to negligible loss during their formation a remarkably coherent relationship between cr and co and an associated ni co correlation indicate the variable presence of a minor ultramafic component having an atypically low cr co ratio there is compelling evidence indicating that the layered tektites formed as sheets or pools of melt because there are severe difficulties with the impact transport of melt 600 km their distribution across a field 1140 km in length is inconsistent with their formation in a single crater maintenance of the melt in a liquid state required that it remained in the fireball until it neared the ground thus layered tektites should be deposited within a few crater radii of their parent craters and many craters are required to account for their distribution across a field 1140 km long confirmation of this model can be obtained by discovering the predicted km size craters or by demonstrating that extensive and widely separated regions yield only layered tektites and were thus covered with continuous melt sheets ejected from independent craters

a review of the occurrences and causes of migration contamination in crude oil abstract migration contamination occurs when a migrating or trapped crude oil functions as a solvent dissolving molecular components from the syndepositional organic matter of the migration conduit and or the reservoir rock this review documents the causes and worldwide occurrences of migration contamination and suggests methods of identifying the signatures of this phenomenon within the molecular and isotopic composition of crude oils instances of migration contamination have been identified in oils of australia asia africa and north america and are best identified by the presence of molecular and or isotopic imbalances in the oil such imbalances are most apparent when co occurring molecular suites are incompatible with one another particularly in terms of thermal maturity occurrences of migration contamination in oils of the us gulf of mexico documented by molecular maturity imbalances such as the presence of unsaturated hydrocarbons known to be unstable at petroleum generation temperatures provide the best examples of this phenomenon an attempt is made to quantify the extent and impact of this process in the vermilion 14 field offshore louisiana in the us gulf of mexico here molecular maturity markers in the migrated fluid and in the syndepositional organic matter of the reservoir rocks are compared and the proportion of contamination in each reservoired fluid is estimated examples such as this may assist in explaining maturity anomalies observed in several oils worldwide particularly in tertiary reservoired oils that have migrated through and are trapped in thermally immature sediments it is suggested that the low molecular maturity ratios often observed in tertiary reservoired oils and attributed to unusually high heating rates may be caused at least in part by migration contamination

geochemical characterization of qhd29 oils on the eastern margin of shijiutuo uplift bohai sea china insights from biomarker and stable carbon isotope analysis abstract toc and rock eval analyses were conducted on cutting samples 111 from various paleogene formations ed3 es1 and es3 in the qinnan sag the average values of total organic carbon toc content are 1 11 1 64 and 2 29 for ed3 es1 and es3 samples respectively the es1 and es3 source rocks are of relatively high s2 values ranging from 0 42 to 46 01 and 2 46 61 01mghc rock respectively the ed3 rocks have lower generative potential with s2 values ranging from 0 9 to 9 3 mg hc g rock moreover tmax values indicate that these source rocks are sufficiently mature for petroleum generation these analyses suggest that es1 and es3 are potential source rocks for oils produced from the qhd29 field eighteen oil samples from the qhd29 field were analyzed by gc and gc ms and 84 qhd29 oil 13 and source rock 71 samples were employed for stable carbon isotope analysis based on hierarchical cluster analysis of selected biomarker parameters the qhd29 oils can be identified into two groups group i and group ii oils are both derived from the eocene shahejie formation es1 and es3 displaying remarkable difference to the oligocene ed3 derived oils in comparison with group ii oils group i oils display relatively low 4msi and high g h indicating that group i oils have important contributions from es1 source rock deposited under more alkaline saline environment moreover these two group oils can be clearly separated by 13c values and group i oils are isotopically lighter than group ii oils difference occurs in stable carbon isotope distribution between es1 and es3 source rock extracts as well and es1 source rocks are characterized by relatively light carbon isotopic composition this implies that group i oil shares more es1 derived oil which is consistent with the results of biomarker analysis

origin and accumulation mechanisms of petroleum in the carboniferous volcanic rocks of the kebai fault zone western junggar basin china abstract the kebai fault zone of the west junggar basin in northwestern china is a unique region to gain insights on the formation of large scale petroleum reservoirs in volcanic rocks of the western central asian orogenic belt carboniferous volcanic rocks are widespread in the kebai fault zone and consist of basalt basaltic andesite andesite tuff volcanic breccia sandy conglomerate and metamorphic rocks the volcanic oil reservoirs are characterized by multiple sources and multi stage charge and filling history characteristic of a complex petroleum system geochemical analysis of the reservoir oil hydrocarbon inclusions and source rocks associated with these volcanic rocks was conducted to better constrain the oil source the petroleum filling history and the dominant mechanisms controlling the petroleum accumulation reservoir oil geochemistry indicates that the oil contained in the carboniferous volcanic rocks of the kebai fault zone is a mixture the oil is primarily derived from the source rock of the permian fengcheng formation p 1 f and secondarily from the permian lower wuerhe formation p 2 w compared with the p 2 w source rock p 1 f exhibits lower values of c 19 tt c 23 tt c 19 20 tt tt ts ts tm and 20r sterane c 27 c 28 ratios but higher values of tt c 23 c 21 hhi gammacerane c 30 hopane hopane 20s c 34 c 33 c 29 and c 29 20s 20s 20r ratios three major stages of oil charge occurred in the carboniferous in the middle triassic late triassic to early jurassic and in the middle jurassic to late jurassic periods respectively most of the oil charged during the first stage was lost while moderately and highly mature oils were generated and accumulated during the second and third stages oil migration and accumulation in the large scale stratigraphic reservoir was primarily controlled by the top carboniferous unconformity with better porosity and high oil enrichment developed near the unconformity secondary dissolution pores and fractures are the two major reservoir storage space types in the reservoirs structural highs and reservoirs near the unconformity are two favorable oil accumulation places the recognition of the large scale carboniferous volcanic reservoirs in the kebai fault zone and understanding of the associated petroleum accumulation mechanisms provide new insights for exploring various types of volcanic reservoir plays in old volcanic provinces and will undoubtedly encourage future oil and gas exploration of deeper strata in the region and basins elsewhere with similar settings

application of 24 norcholestanes for constraining source age of petroleum abstract two c26 sterane ratios the 24 nordiacholestane ratio ndr and the 24 norcholestane ratio ncr are useful for assessing petroleum source age values for these parameters generally increase in the cretaceous when diatoms were rapidly radiating and further in the oligo miocene due to widespread high latitude deposition of diatomaceous sediments sources with shale lithologies tend to exhibit the highest ratios while carbonate and terrigenous rich lithologies generally show lower ratios on the north slope of alaska elevated ratios are observed for cretaceous hrz oils and mixed oils containing cretaceous input compared to older triassic and jurassic derived oils tertiary sourced oils from romania and bulgaria have much higher ratios relative to jurassic sourced oils in the black sea region oleanane was observed in comparable levels in some black sea tertiary and jurassic oils and source rocks ndr and ncr coupled with other age diagnostic indicators such as oleanane and dinosterane provide powerful tools for differentiating age of source and organic facies for oils from the black sea and sub andean basins of peru and ecuador respectively oils derived from sources deposited in low tropical latitudes tend to have little diatom input and as a consequence do not display high values regardless of age

application of biological markers in the recognition of palaeohypersaline environments the hydrocarbon fractions of a marl sample from a messinian basin in the northern appenines and four oils rozel point oil utah and three seep oils from sicily were studied

variability of petroleum inclusions in vein fossil and vug cements a geochemical study in the barrandian basin lower palaeozoic czech republic abstract although no commercial oil or gas occurrences have been found in the barrandian basin residual oils and petroleum inclusions give evidence about the petroleum history of this lower palaeozoic basin petroleum inclusions are hosted in six generations of calcite and quartz cements that can be attributed to different stages of a basinal cycle and associated diagenetic events they were analysed using an on line crushing and an off line crush and leach approach five different groups pi a to pi e and intermediate mixtures pi m could be differentiated based on the relative distribution of n alkanes all oils had a calculated aromatic maturity rc ranging between 0 9 and 1 6 pi a shows a molecular weight maximum in the range of n c8 11 with a constant attenuation towards higher carbon numbered n alkanes this distribution is interpreted as the pristine precursor oil for other petroleum inclusion groups pi b has a maximum weight abundance at n c15 20 the genetic relationship between pi b and pi a can tentatively be explained by mixing effects or by gas stripping pi c is bimodal and characterised by a molecular weight maximum at n c32 34 and also a molecular weight maximum at n c15 20 similar to that of group pi b pi d shows a normally distributed molecular weight maximum in the range n c25 28 and is interpreted as a wax precipitate from ascending gas saturated in n alkanes pi e contains predominantly gaseous compounds with only a few higher hydrocarbons thompson s aromaticity values are elevated for condensates of group pi e and also for group pi c that is dominated by long chained n alkanes this gives evidence that fault bound petroleum migration in the barrandian basin was associated with evaporative fractionation for group pi c and pi e samples of group pi e yielded gas range compounds only and all come from a last generation of vein filling whitish calcite that was formed in a late uplift phase of the basin for other petroleum inclusion groups only a vague preferential occurrence in specific mineralisation phases or stratigraphic intervals of the host rock has been found this reflects the predominance of fracture bound migration in the barrandian basin aromatic maturity values also showed no correlation between either crystal type or pi group in six of the investigated petroleum inclusion samples alk 1 enes are present these terminal olefins are interpreted to be the result of the natural pyrolysis of petroleum due to the intrusion of volcanic dykes or hydrothermal processes an artificial generation of olefins during sample work up and analysis is unlikely the preservation of alk 1 enes from palaeozoic times was possible due to the protecting environment of petroleum inclusions

oil source rock correlation of the lower paleozoic petroleum system in the baltic basin northern europe the correlation of lower paleozoic marine source rocks with reservoired oils by biomarkers is complex because of the uniform early phanerozoic biomass bacteria and algae and the lack of land plant and animal input accordingly the main source rocks for the most prolific oil province in the baltic basin are still a matter of debate the 10 source rocks and 15 oil samples from 5 northern european countries bordering the baltic sea basin were analyzed by gas chromatography gc with flame ionization detector gc mass spectrometry gcms and gcms ms to detect acyclic isoprenoids and aliphatic aromatic and nitrogen sulfur and oxygen biomarkers chemometric tools were applied to screen for meaningful source and age related biomarkers and to highlight genetics extended tricyclic terpane ratios c24 tetracyclic terpane c26 tricyclic terpane ratios and relative c29 sterane concentrations are considered the most promising biomarkers in differentiating llandovery shales from cambrian to ordovician alum shale and for correlation with expelled oil the uranium irradiation related c26 c28 triaromatic steroid concentrations provide possible distinguishing criteria for the source potential of the different alum shale units enhanced oil maturation by volcanic intrusion is highlighted by sterane biomarkers and polycyclic aromatic hydrocarbons the alum shale is here considered the main source rock for oil accumulations in lower paleozoic reservoirs of the baltic basin oil seepage occurring in ordovician limestone was mainly generated by the middle cambrian alum shale and middle cambrian sandstone reservoirs were mainly sourced by upper cambrian and lower ordovician alum shale with higher maturity considerations about the assessment of migration distance are based on carbazole concentrations and c29 sterane isomerization advanced studies to unravel detailed lower paleozoic oil source rock correlations are based on meaningful biomarkers offer approaches to significantly reduce the exploration risk in this area and could be applied to similar early paleozoic petroleum systems in other basins

oleanane or lupane reappraisal of the presence of oleanane in cretaceous tertiary oils and sediments nonpolar gc columns are normally used for gc ms analysis of saturate fractions from crude oils under these conditions lupane coelutes with oleananes and some minor c30 compounds of non terrigenous origin having lupane like mass spectra because any peak eluting fractionally earlier than 17 21 h hopane in the m z 191 mass chromatogram is routinely assigned to oleanane the presence of lupane may sometimes have been overlooked lupane and oleananes are easily separated using reverse phase hplc triterpane concentrates from 10 crude oils known to contain oleananes were hplc separated lupane was unambiguously identified in six of the oils by full scan gc ms analysis of fractions having the hplc retention time of authentic lupane gc separation of lupane and oleananes is possible using polar gc columns having a polyethylene glycol stationary phase organic geochemistry 23 1995 21 allowing estimation of the lupane lupane oleanane ratio high ratios were measured in the marraat oil west greenland 0 8 and the amauligak oil from the beaufort mackenzie delta 0 26 the results suggest that lupane may be more frequently occurring than previously thought and that this compound is preferably associated with high latitude samples high concentrations of 28 nor and 24 28 bisnortriterpanes oleananes lupanes and taraxastanes were detected in the marraat oil

impact induced melting and the development of large igneous provinces abstract we use hydrodynamic modelling combined with known data on mantle melting behaviour to examine the potential for decompression melting of lithosphere beneath a large terrestrial impact crater this mechanism may generate sufficient quantity of melt to auto obliterate the crater melting would initiate almost instantaneously but the effects of such massive mantle melting may trigger long lived mantle up welling that could potentially resemble a mantle hotspot decompression melting is well understood it is the main method advocated by geophysicists for melting on earth whether caused by thinned lithosphere or hot rising mantle plumes the energy released is largely derived from gravitational energy and is outside but additive to the conventional calculations of impact modelling where energy is derived solely from the kinetic energy of the impacting projectile be it comet or asteroid the empirical correlation between total melt volume and crater size will no longer apply but instead there will be a discontinuity above some threshold size depending primarily on the thermal structure of the lithosphere we estimate that the volume of melt produced by a 20 km diameter iron impactor travelling at 10 km s may be comparable to the volume of melt characteristic of terrestrial large igneous provinces 106 km3 similar melting of the mantle beneath an oceanic impact was also modelled by roddy et al int j impact eng 5 1987 525 the mantle melts will have plume like geochemical signatures and rapid mixing of melts from sub horizontal sub crater reservoirs is likely direct coupling between impacts and volcanism is therefore a real possibility that should be considered with respect to global stratigraphic events in the geological record we suggest that the end permian siberian traps should be reconsidered as the result of a major impact at 250 ma auto obliteration by volcanism of all craters larger than 200 km would explain their anomalous absence on earth compared with other terrestrial planets in the solar system

application of aromatic compounds as maturity indicators in source rocks and crude oils concentration ratios of aromatic compounds such as naphthalenes phenanthrenes and dibenzothiophenes are at present attracting increasing attention as maturity indicators in sedimentary rocks and crude oils generally these indicators rely either on an increase with maturity in the degree of alkylation of a given parent compound or a shift in the isomer distribution of alkyl aromatic homologues towards thermally more stable isomers a combination of both concepts in the methylphenanthrene index mpi resulted in an excellent maturity parameter as demonstrated for rock extracts by an improved correlation with mean vitrinite reflectance rm between 0 65 and 1 4 i e in the zone of oil formation in cases that rm measurements were ambiguous this empirical relationship has proved useful in the calculation of theoretical vitrinite reflectance rc values from the mpi on the other hand for potential petroleum source rocks reaching maturity at relatively low temperatures the influence of the organic matter type on the aromatic distributions cannot be neglected consequently organic facies effects should be taken into account in the interpretation of aromatic distributions of such source rocks and related crude oils since the impact of the organic facies is strongly reduced with increasing maturity aromatic maturity parameters are particularly useful in the maturity evaluation of post mature crude oils and condensates in contrast to biological markers substantially higher concentrations of the key alkyl aromatics persist at elevated maturation levels thus aromatic maturity parameters should be considered as versatile tools in organic maturation studies and can complement established maturity indicators based on steranes and terpanes

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

application of tetracyclic polyprenoids as indicators of input from fresh brackish water environments abstract c30 tetracyclic polyprenoids tpp are most prominently observed in samples derived from low salinity i e fresh to brackish lacustrine environments and are generally present in low levels in samples derived from saline i e marine and saline lacustrine environments a near shore facies of the chonta formation peru that has no marine palynomorphs but abundant chlorococcalean green algal nonmarine palynomorphs has high levels of tpp suggesting green algae or chlorophyta are a possible source for the tpp compounds the ratio between a c30 tpp compound and 27 norcholestanes is useful for assessing this nonmarine algal input moderate elevations of tpp above what is common in marine derived samples were found in ostensibly marine source rocks and oils from certain basins of western and northern south america middle magdalena colombia maracaibo venezuela and trinidad basins this is likely due to transport from the nonmarine to the marine environment because of an influx of fresh water into the near shore marine environment alternatively oils from these basins may have inputs from near shore shallow marine algae with chemistry similar to that found in lacustrine settings the tpp ratio in conjunction with other environmental indicators such as 4 methyl steranes or hopane sterane ratio is useful for differentiating marine and nonmarine influences in pre salt oils and source rocks of west africa the tpp ratio used with other environmental indicators gammacerane c29 steranes c30 steranes and age diagnostic biomarkers dinosteranes 4 methylsteranes can be useful in differentiating among nonmarine source facies for example in the turpan hami basin china permian saline lacustrine and jurassic lacustrine deltaic facies can be discriminated

occurrence and geochemical significance of 1 2 5 6 tetramethylnaphthalene analysis of aromatic hydrocarbon fractions of selected coal and shale samples reveals the predominance of two specific polyalkylnaphthalenes which have been identified as 1 2 5 trimethylnaphthalene and 1 2 5 6 tetramethylnaphthalene the maturity of the samples is such that the source effect on the formation of individual molecules from biological precursors is expected to be recognisable these alkylnaphthalenes are thought to be diagenetically derived from pentacyclic triterpenoids via 8 14 seco triterpenoids which are also detectable in some of the samples investigated it is proposed that 1 2 5 6 tetramethylnaphthalene in the coal samples is formed by cleavage and methyl shift reactions from geminal c 4 methylated triterpenoids which contain a leaving group in position 3 for the shale samples degradation of monoaromatic secohopanoids must be considered as an alternative pathway

organic geochemical characteristics and organic matter enrichment of mudstones in an eocene saline lake qianjiang depression hubei province china abstract the qianjiang depression is a typical eocene hypersaline lake basin developing good source rocks in the qianjiang formation which have recently been identified as a potential target for saline lacustrine shale oil exploration previous studies have only focused on estimates of source rock potential and reservoir quality however studies on organic matter enrichment mechanisms in evaporative environments are limited based on organic geochemical and mineralogical data as well as sedimentological analyses we researched the factors controlling differences in organic matter enrichment in the basin the results show that total organic carbon toc contents are closely associated with lithofacies with distinct variations three main lithofacies associations las were identified 1 glauberite rich la1 with medium toc 2 carbonate rich la2 with high toc and 3 anhydrite rich la3 with low toc the distribution of biomarkers from 14 samples indicate both higher land plants and aquatic organisms were involved in the organic matter accumulations combining experimental results on gammacerane c30 hopane extended tricyclic terpane ratio etr sr ba v ni and sedimentary characteristics we analyzed the sedimentary environments of the three las la1 was deposited in a salinity stratified waterbody with strong evaporation la2 was deposited in a still stratified deep waterbody whereas la3 was deposited in a disturbed saline waterbody sedimentary environments not only controlled the formation of the lithofacies but also influenced the organic matter sources and preservation relatively low salinity strong anoxic condition without physical disturbance appropriate nutritional terrigenous material inputs and algal blooms produced the best organic matter enrichment in the saline lake system

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

hydrocarbon generating potential and accumulation contribution of the fourth member of the shahejie formation in the liaodong bay sub basin bohai bay basin abstract the liaodong bay sub basin is one of the most petroliferous sub basins in the bohai bay basin the fourth member of the eocene shahejie formation e 2 s 4 50 5 42 ma which is an important source rock interval in other sub basins was rarely studied in the liaodong bay sub basin the hydrocarbon generating potential biomarker assemblage and accumulation contribution for discovered oil fields of the e 2 s 4 source rock interval in the liaodong bay sub basin were studied using geological and geochemical data the e 2 s 4 source rocks in the liaodong bay sub basin display relatively high total organic carbon contents toc and rock eval hydrogen indices hi and can be considered as a set of excellent oil prone tendency source rocks the source rocks interval is characterized mainly by relatively low pristane phytane pr ph c 19 c 23 tricyclic terpane c 19 c 23 tt c 24 tetracyclic terpane c 26 tricyclic terpane c 24 tet c 26 tt low to medium hopane sterane h s medium 4 methyl steranes c 29 steranes ratio 4 ms c 29 st c 35 22s c 34 22s hopane c 35 c 34 sh and high gammacerane c 30 hopane g h extended tricyclic terpane ratio etr c 28 tt c 29 tt c 28 tt c 29 tt ts and were deposited in anoxic to sub oxic saline water environment with no or minor terrigenous organic matter and medium dinoflagellate input the maturity of e 2 s 4 source rocks in the liaozhong and north liaoxi sags is too high to provide oils for fields the e 2 s 4 source rocks in the south and middle liaoxi sag displayed opportune maturity within the oil window and were proved by oil source correlation having important accumulation contribution for discovered oil fields in this area the e 2 s 4 derived oils should be taken seriously in the future exploration in the south and middle liaoxi sag and on adjacent uplifts

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

tetracyclic polyprenoids indicators of freshwater lacustrine algal input because of the great variety of lacustrine source depositional characteristics and biological consortia identification of a universally applicable indicator of freshwater or brackish water organic input for crude oils and rock extracts has proven elusive tetracyclic polyprenoid compounds tpp are present in relatively high concentrations in oils and associated source rocks deposited under freshwater or brackish water conditions but typically are present in relatively low concentrations in samples from marine or coal forming depositional environments a tpp ratio constructed from the gas chromatography tandem mass spectrometry peak areas of a c30 tetracyclic polyprenoid divided by the sum of the peak areas of the c26 27 norcholestanes revealed great specificity in identifying freshwater or brackish water algal input particularly in crude oils

quantitative evaluation of the oil leg potential in the oliver gas field timor sea australia oil bearing fluid inclusions in sandstone cores and cuttings represent hidden oil shows the frequency of quartz grains containing these inclusions the goi number reflects the maximum paleo oil saturation experienced in a sandstone reservoir irrespective of the present fluid phase samples that have been exposed to high oil saturation have goi numbers at least one order of magnitude greater than samples that have demonstrably low oil saturation in this way these fluid inclusion data can be used to identify paleo oil columns and to map original oil water contacts in wells where oil has been displaced by a later gas charge moreover the use of detailed goi mapping to accurately define the location of the original oil water contact allows the height of the paleocolumn to be determined and an estimate to be made of original oil in place the oliver oil and gas discovery located in the timor sea australia presently contains a hydrocarbon column of 178 5 m composed of 164 m of gas over a 14 5 m oil leg and is filled to spillpoint in well oliver 1 goi mapping has delineated a gross paleo oil column of between 99 and 132 m within the present gas leg this corresponds to original oil in place of up to 200 million bbl considerably greater than the 45 million bbl of oil presently reservoired the displacement of up to 155 million bbl of oil from this structure has high graded the prospectivity of tilted fault blocks updip from the oliver structure goi mapping is an innovative approach to reservoir characterization that can reliably detect paleo oil accumulation in hydrocarbon traps that are presently filled by gas these data allow the oil leg potential of both gas discoveries and nearby untested structures to be addressed in a quantitative manner before additional drilling is commissioned

charging of oil fields surrounding the shaleitian uplift from multiple source rock intervals and generative kitchens bohai bay basin china abstract this paper discusses origin and charging directions of oil fields on the shaleitian uplift bohai bay basin the shaleitian uplift is a footwall uplift surrounded by three sags containing mature source rocks the origins of the four oil fields on the shaleitian uplift both in terms of source rock intervals and in terms of generative kitchens were studied using biomarker distributions for 61 source rock samples and 27 oil samples hierarchical cluster analysis using 12 parameters known to be effective indicators of organic matter input and or depositional conditions allowed the identification of six oil types or classes these six oil classes could then be linked to three distinct source rock intervals ranging in age from 43 0 ma to 30 3 ma the third member 43 0 38 0 ma in age and first member 35 8 32 8 ma of the eocene shahejie formation and the third member of the oligocene dongying formation 32 8 30 3 ma each sourced one class of oil the other three classes represent mixtures of oil generated from multiple source rock intervals traps on the shaleitian uplift were charged in the east by oil generated from the eocene shahejie formation in the bozhong sag in the southeast by oil generated from the eocene shahejie and then oligocene dongying formations in the southwestern part of the bozhong sag and or in the eastern part of the shanan sag and in the southwest by oil generated from the eocene shahejie formation in the western part of the shanan sag the estimated migration distances range from less than 5 km to about 20 km the compositional heterogeneity within fields and multiple parameter comparisons between oils from nearby wells in different fields have proven to be a powerful tool to determine the in filling histories of oil fields in cases where multiple source rock intervals and multiple generative kitchens exist

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

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

constraining the oil charge history of the south pepper oilfield from the analysis of oil bearing fluid inclusions abstract the south pepper oilfield located in the barrow sub basin on the nw margin of the australian continent has experienced a multi phase charge history abundant oil bearing fluid inclusions are present in samples from within the current gas cap suggesting that an oil column existed prior to gas this palaeo oil gas leg fi oil has ts tm and c29 c30 hopane ratios of 1 and the c35 homohopanes are a significant proportion of the extended homohopanes it has lower pr ph and diasterane sterane ratios than the currently reservoired live oil and contains gammacerane a series of peaks tentatively identified as c30 to c34 17 h 30 norhopanes and a large amount of 2 methylhopanes collectively geochemical analysis of the gas leg fi oil suggests that it was generated from a less mature more calcareous source rock deposited under more reducing conditions than the upper jurassic dingo claystone the main source of the live oil in addition the presence of c30 dinosteranes in the gas leg fi oil provides a triassic or younger age constraint this makes palaeozoic carbonates an unlikely source possible source intervals for the gas leg fi oil are thin lower jurassic limestones and marls which occur at the base of the lower dingo claystone or a thin limestone unit the cunaloo member at the base of the triassic locker shale samples from within the present oil leg also contain abundant oil inclusions consistent with high oil saturations at the present day however these oil inclusions exhibit different fluorescence colours suggesting they represent a second oil charge geochemically the oil leg fi oil has an intermediate composition between the live oil and the gas leg fi oil suggesting that gas charge displaced the first oil charge samples of which were preserved as fluid inclusions in the oil leg sample biodegradation of the first oil charge indicated by the presence of 17 h 25 norhopanes in the currently reservoired live oils can be attributed to the ingress of meteoric waters probably during sub aerial exposure of the basin margin during miocene wrenching changing environmental conditions curtailed bacterial activity and allowed unaltered oil sourced from the dingo claystone to accumulate below the gas cap and mix with the biodegraded residues of the first oil charge to achieve the live oil composition the biodegradation event must have preceded the second charge as the live oil contains compounds such as n alkanes which would have been removed had alteration occurred after the second charge complex charge histories are common and the analysis of palaeo oils trapped within fluid inclusions provides the opportunity to achieve a more comprehensive assessment of hydrocarbon charge

australasian impact crater buried under the bolaven volcanic field southern laos the crater and proximal effects of the largest known young meteorite impact on earth have eluded discovery for nearly a century we present 4 lines of evidence that the 0 79 ma impact crater of the australasian tektites lies buried beneath lavas of a long lived 910 km3 volcanic field in southern laos 1 tektite geochemistry implies the presence of young weathered basalts at the site at the time of the impact 2 geologic mapping and 40ar 39ar dates confirm that both pre and postimpact basaltic lavas exist at the proposed impact site and that postimpact basalts wholly cover it 3 a gravity anomaly there may also reflect the presence of a buried 17 13 km crater 4 the nature of an outcrop of thick crudely layered bouldery sandstone and mudstone breccia 10 20 km from the center of the impact and fractured quartz grains within its boulder clasts support its being part of the proximal ejecta blanket

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

origin of petroleum accumulation in the chaheji gaojiapu structural belt of the baxian sag bohai bay basin china insights from biomarker and geological analyses abstract the origin of petroleum accumulations in the chaheji gaojiapu structural belt of the baxian sag bohai bay basin was evaluated based on the results of rock eval pyrolysis on 135 samples and a biomarker analysis on 26 source rock samples and 33 oil samples the four possible source rock intervals have different biomarker assemblages and were deposited in different environments for example pristane phytane c27 diasterane c27 sterane and c19 c23 tricyclic terpane ratios show an increasing trend but c28 c29 tricyclic terpane c28 c29 tricyclic terpane ts and steranes hopanes parameters display a decreasing trend among the lower part of the first member es1l and the middle es3m and lower part es3l of the third member of the eocene shahejie formation this finding indicates that a decreasing anoxic and alkaline environment with an increasing input of terrigenous organic matter developed during the deposition of the es1l es3m and es3l source rocks however the biomarker parameters of the forth member es4 of the eocene shahejie formation display highly similar characteristics with the es3l source rocks except for the c29 sterane 20s 20s 20r and c27 diasterane c27 sterane ratios which show obviously higher than the other source rock values the es3 derived oils are absolutely dominant in the chaheji gaojipu structural belt based on the biomarker analysis of saturated hydrocarbon with slight or no contributions from the es1l and es4 source rocks because of the low maturation for the es1l source rock and the absence of vertical migrating channels for the es4 source rock faults are vital to petroleum migration and accumulation in this area and demonstrate the following double effects 1 the deep faults cutting off the es3 source rocks are the key channels for oil vertical migration 2 the shallow faults entrap oil and finally form the commercial oil pools as a result the fault block reservoir is the major oil reservoir type in the chaheji gaojiapu structural zone and the lithologic reservoir is another oil reservoir type in this area based on 1d burial and thermal history modelling the e3 and e4 source rocks reached the oil generation peak at approximately 5 ma and 20 ma respectively but the es1l source rock is still in the low mature stage therefore the process of the large oil migration and accumulation for the es3 source rocks occurred during the late neogene quaternary through this research there are two considerable exploration potentials for this area including condensate reservoirs in the deep strata and low mature reservoirs in the es1 stratum interval

geographic variation in australasian microtektite concentrations implications concerning the location and size of the source crater geographic variations in the concentration of australasian microtektites in 42 cores from the indian ocean western equatorial pacific ocean and the philippine celebes and sulo seas were used to predict the location of the australasian tektite source crater and to estimate its size the location that seems to best explain the geographic variations in microtektite concentrations is located in central cambodia at about 12 n latitude and 106 e longitude the diameter of the source crater is estimated to be between 32 and 114 km based on thickness of the microtektite layer at each site and distance from the predicted source area in cambodia the large range in estimated size of the source crater is due to a lack of knowledge about the value of the exponent that describes the radial decrease in ejecta thickness additional microtektite ejecta bearing sites closer to the source region could help resolve this problem

impacts do not initiate volcanic eruptions eruptions close to the crater many papers on meteorite impact suggest that large impacts can induce volcanic eruptions through decompression melting of the underlying rocks we perform numerical simulations of the impact of an asteroid with a diameter of 20 km striking at 15 km s 1 into a target with a near surface temperature gradient of 13 k km 1 cold case or 30 k km 1 hot case the impact creates a 250 300 km diameter crater with 10 000 km3 of impact melt however the crater collapses almost flat and the pressure field returns almost to the initial lithostat even an impact this large cannot raise mantle material above the peridotite solidus by decompression statistical considerations also suggest that impacts cannot be the common initiator of large igneous provinces any time in post heavy bombardment earth history

geochemical comparison of oil bearing fluid inclusions and produced oil from the toro sandstone papua new guinea abstract a detailed study was carried out to compare the geochemistry of the crude oil in the lower cretaceous toro sandstone reservoir in the iagifu 7x well with oil trapped in fluid inclusions in this sandstone in the iagifu 7x and p nyang 2x wells in the papuan fold belt the drill stem test dst oils and the oils trapped in fluid inclusions show different source and maturity dependent geochemical parameters biomarkers suggest that the dst oils at iagifu 7x were derived from clay rich mixed marine terrestrial source rocks deposited under oxic conditions probably middle to late jurassic mudstones the fluid inclusion oils were derived from a less terrestrially influenced marine source rock deposited under less oxic conditions the fluid inclusion oils contain 1 2 7 trimethylnaphthalene and oleanane biomarkers indicative of angiosperm input and a cretaceous or younger source rock these oils are more mature calculated reflectance rc 1 02 than the reservoired oil at iagifu 7x rc 0 84 and condensate at p nyang 2x rc 0 84 source and thermal maturity parameters for all three fluid inclusion samples are similar suggesting that they were derived from similar source rock facies furthermore samples with predominantly blue vs white fluorescing oil inclusions have no discernible geochemical maturity difference suggesting that the use of fluorescence colours as a qualitative guide to the maturity of the trapped oil is not valid in this case fluid inclusion oils were trapped prior to charge of the reservoir with oil at the iagifu 7x and gas condensate at the p nyang 2x wells the fluid inclusion oils therefore represent an early oil charge from a deeply buried probably cretaceous source rock which started migrating into the toro sandstone during the miocene at iagifu this early oil was probably diluted by a larger volume of jurassic oil generated at the end of the miocene the absence of fluid inclusions with compositions like the currently reservoired oil is interpreted to be due to oil charging an already oil saturated zone when diagenesis is likely to have been inhibited at the p nyang well the transition from oil as represented by the oil inclusions to gas condensate was most likely caused by gas displacement

depositional environment and factors controlling β carotane accumulation a case study from the jimsar sag junggar basin northwestern china abstract a combined investigation of bulk geochemistry and molecular geochemistry was carried out on 31 source rock samples from the lower permian lucaogou formation in the jimsar sag of the junggar basin northwestern china geochemical characterization reveals the depositional environments and other factors favorable for the generation and accumulation of carotane an important hydrocarbon precursor many core samples have a total organic carbon content 1 and rock eval s2 values 2 mg hc g rock suggesting relatively high hydrocarbon generation potential biomarkers in the lucaogou source rock extracts are characterized by short to long chain n alkanes a wide range of pr ph ratios 0 74 1 42 and carotane index values carotane cmax 0 16 1 92 high concentrations of c29 sterane relatively low tricyclic terpane content and moderate gammacerane index values 0 14 0 29 this is consistent with a weakly oxidizing to weakly reducing depositional environment with fresh to brackish water conditions rapid input of terrigenous organic matter and a relatively small contribution of aquatic algal bacterial organic matter cross plots of biomarker parameters and the carotane index show that carotane in the lucaogou source rocks is mainly derived from terrigenous organic matter and is found predominantly in sediments deposited in weakly reducing brackish environments it does not appear to have been affected by thermal maturation