a terra rossa like paleosol complex from the upper jurassic of portugal the basal upper jurassic unconformity in the lusitanian basin of portugal commonly exhibits an irregular palaeokarstic surface developed in underlying middle jurassic carbonates in the serra da arrabida area south of lisbon wire cut quarry faces expose a thick upper jurassic paleosol complex overlying fissured and brecciated limestone veneered with a calcrete crust and associated with colluvial deposits the paleosol complex is a red mudstone with calcrete stringers which superficially resembles present day red mediterranean terra rossa soils a detailed micromorphological study indicates the absence of any clay illuviation in the paleosol unit which suggests that it is not comparable to the true terra rossa alfisols but more closely resembles present day aridisols this difference from true terra rossa soils probably reflects formation under a drier climate which is confirmed by the occurrence elsewhere in portugal of evaporitic lake deposits of the same age the paper stresses the role of soil petrography micromorphology in interpreting pedogenesis in paleosols

hierarchal genetic stratigraphy a framework for paleoceanography a detailed genetic stratigraphic framework for paleoceanographic studies can be derived by describing correlating interpreting and predicting stratigraphic sequences relative to a hierarchy of their constituent time stratigraphic transgressive regressive units t r units t r unit hierarchies are defined and correlated using lithostratigraphic and paleoecologic data but correlations can be enhanced or checked tested to confirm or deny with objective biostratigraphic magnetostratigraphic or chemostratigraphic data such chronostratigraphies can then be bracketed by radiometric ages so that average periodicities for t r units can be calculated and a hierarchal geochronology derived t r units are inferred to be the net depositional result of eustatic cycles of sea level change and can be differentiated from autocyclic deepening shallowing units because the latter are noncorrelative intrabasinally boundaries between t r units are conformable or unconformable genetic surfaces of two types transgressive surfaces and climate change surfaces the latter are useful for correlating minor transgressive phases through nonmarine intervals thereby deriving information linking paleoclimatic and paleoceanographic processes permo carboniferous sequences can be analyzed relative to a hierarchy of six scales of genetic t r units having periodicities of 225 300 m y first order 20 90 m y second order 7 13 m y third order 0 6 3 6 m y fourth order 300 500 10 years fifth order and 50 130 10 years or less sixth order paleogeographic maps for the time of maximum transgression transgressive apex of successive fifth order t r units 5 25 m thick in the glenshaw formation upper pennsylvanian northern appalachian basin delineate delta lobes embayments islands and linear seaways relative extent of marine inundation on the fifth order maps was used to delineate fourth order t r units and the fourth order t r units constitute the transgressive half of a third order t r unit this third fourth and fifth order hierarchy is correlated more than 1200 km 750 miles to the western interior basin and is confirmed with limited objective biostratigraphy

origins of heavy oils in the erlian basin ne china abstract the erlian basin is located in the central asia mongolian fold belt between the siberian and sino korean cratons it is a mesozoic continental rift basin composed of 52 individual fault depressions the main phase of rifting took place during the early cretaceous when a series of fluvial lacustrine sediments were deposited each depression forms an independent sedimentary system and behaves as an independent petroleum system hydrocarbon source rocks are found in the upper arshan and lower tengger formations these are mainly type ii source rocks and are mainly located in oil generation window at the present day a series of oilfields and commercial oil flows have been found in the basin highlighting its good petroleum potential many of these oils are heavy six oil samples from the anan and ten from the jirgalangtu depressions have been subjected to routine geochemical analytical techniques in order to evaluate the origins the methods used include gas chromatography of the saturated and aromatic hydrocarbon fractions gas chromatography mass spectrometry of the saturated hydrocarbon fraction and stable carbon isotope analyses the trace metal elements of the biodegraded oils from the jirgalangtu depression were also analysed by atomic absorption spectroscopy two types of heavy oils primary and biodegraded were identified on the basis of these data the former includes both immature and mature heavy oils a filtering and spill process was proposed to explain the origin of primary mature heavy oils or tar mat in the anan depression the biodegraded oils from the jirgalangtu depression were ranked and classified in terms of the degree of biodegradation using a series of geochemical parameters based on the gas chromatographic concentrations and biomarker fingerprints of gas chromatography mass spectrometry of the saturated hydrocarbon fraction the relationship between oil saturation and porosity indicates that the heavy oils in the jirgalangtu depression were biodegraded after they accumulated

sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

geochemical characterisation of fika formation in the chad bornu basin northeastern nigeria implications for depositional environment and tectonic setting late cretaceous shales of the fika formation in the chad bornu basin northeastern nigeria were analysed to define paleoenvironment and source of the organic matter and their relation to tectonic setting the organic carbon and sulphur contents of fika shale samples are in the range of 0 51 2 13 and 0 31 1 65 wt respectively pointing that these shales were deposited in suboxic anoxic marine conditions the biomarker and chemical compositions provide evidence for a major contribution of aquatic algae and microorganisms with minor terrigenous organic matter input moderate salinity stratification and relatively anoxic suboxic bottom water conditions are also likely in the fika shales therefore stratified water column with moderate salinity and relatively anoxic suboxic bottom water conditions have contributed to organic matter om preservation in the fika shale layer fika shale samples are rich in sio2 54 80 wt followed by al2o3 23 75 wt and fe2o3 10 19 wt compared with average shale the analysed shale samples are obviously enriched in al2o3 23 75 wt tio2 1 34 wt and p2o5 0 30 wt indicating that these sediments are rich in clay minerals and represent a good possibility for enhanced organic matter production and enrichment plots of fika shale on bivariate discriminant function diagram suggest an active continental margin setting for the provenance the inferred tectonic setting for the late cretaceous shales of the fika formation of the chad bornu basin is in agreement with the tectonic evolutionary history of the west and central africa during the cretaceous period

calcrete palaeosols from the lower carboniferous llanelly formation south wales abstract three calcrete bearing palaeosol units are described from the lower carboniferous llanelly formation in south wales and are named the tyle r bont pedocomplex the cwm dyar pedoderm and the llanelly pedocomplex these units were formed on semi arid to arid floodplains and are associated with sheet flood stream flood and meandering channel deposits three major processes operated during pedogenesis calcification pedoturbation and solution pedoturbation resulted in the formation of brecciated horizons pseudo anticlinal and prismatic structures and a predominance of disorthic nodules the soils developed in smectite rich clays under a seasonally arid climate resulting in strong argillipedoturbation

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

the petrology and palaeoenvironment of the sortino group miocene of se sicily evidence for periodic emergence the sortino group of carbonates consists of three formations which developed on a shallow marine shelf during tortonian and lower messinian times the two lower formations contain three bioherms and are intercalated with thick volcaniclastic sequences the youngest formation is dominated by shoal water lagoonal and peri tidal carbonates early submarine lithification is well developed within the bioherms and consists of construction by both algae and invertebrates the development of peloidal micrites and isopachous fringe growth superimposed upon these are a series of both meteoric phreatic and vadose textures related to episodic emergence of the bioherms these features include bladed cements showing cathodoluminescence pendent cements brecciation alveolar texture and palaeosols the sicilian strata may be directly correlated with the maltese islands sequence and collectively exhibit the effects of fluctuating mediterranean sea levels at an early stage in the late miocene salinity crisis

chemical characteristics of upper cretaceous turonian jet of the gosau group of gams hieflau styria austria abstract jet and coaly sediments within the upper cretaceous gosau schoenleiten formation were collected from two outcrops near gams hieflau styria austria for comparison additional jet and coal samples from different gosau localities were included in the study the identification of jet as bituminous driftwood collotelinite has been provided by microscopical examination of organic matter kollmann h a and sachsenhofer r f mitt ref geol und palaont landesmuseum joanneum sh 2 1998 223 rock eval analyses revealed enhanced hi and lower t max values of jet compared with the coals and coaly shales the results reflect the higher contents of bituminous organic matter compared to vitrain rich coals of similar maturity in comparison with the coals and coaly shales high amounts of liberated hydrocarbons mg hc g c org are in contrast to generally lower yields of soluble organic matter during extraction with dichloromethane indicating that portions of the hydrocarbons are liberated from lipids loosely bound to kerogen during pyrolysis further differences in n alkane distribution patterns odd over even predominance pristane phytane and pristane n c 17 ratios exist between jet coals and coaly shales the microbial origin of short chain n alkanes presumably resulted from the degradation of the predominant odd numbered long chain n alkanes within the jet the occurrence of biological markers sesqui and diterpenoids within the sediments coaly shales coals and jet samples indicates the origin of terrestrial organic matter from conifers biomarker composition of jet samples indicates enhanced aromatisation of sesqui and diterpenoids these results correspond to enhanced aromatisation of steranes as reflected by generally higher relative contents of triaromatic steroids in the jet because of comparable maturation 0 5 0 6 r r of the coals coaly shales and the jet samples confirmed by the isomerisation of c 31 hopanes and c 29 steranes the increase in aromatisation in the jet is thought to reflect increased contribution of bacteria to organic matter degradation the lack of enrichment of the jet samples in hopanes relative to steranes suggests that enhanced biomarker aromatisation is caused by anaerobic rather than by aerobic bacteria

the character and origin of lacustrine source rocks in the lower cretaceous synrift section congo basin west africa lower cretaceous synrift lacustrine shales from the congo basin west africa have been analyzed with sedimentological and geochemical techniques to characterize source rock quality and identify triggers for deposition of intervals richest in organic carbon the sequence includes a lower active rift section deposited during active faulting and subsidence overlain by an upper late rift section deposited during reduced faulting and subsidence total organic carbon toc averages 2 3 wt throughout the active rift siliciclastic shale section 6 in marls in the lower part of the late rift section and 1 2 in deltaic shales in the upper part of the late rift section organic matter consists of mixed types i and iii kerogen in the active rift shales pure type i kerogen in the late rift marls and a type i and iii mixture in the late rift deltaic shales redox proxies indicate that the deep lake was relatively reducing throughout deposition of the active rift and lower late rift sections therefore enhanced anoxia did not trigger deposition of the richest source rocks decreased sedimentation rates in the late rift do not account for the full increase in toc nor the shift on organic matter type the richest source rocks are associated with high rates of organic productivity and chemical sedimentation indicating that flux of dissolved components to the rift lake including nutrients for algae growth was critical we propose that reduced topography associated with the late rift was necessary for efficient cycling of plant derived carbon into soil carbonate and ultimately the rift lake and for enhancing chemical weathering and nutrient flux

a rendzina from the lower carboniferous of south wales a thin calcrete crust horizon from the lower carboniferous llanelly formation of south wales consists of two parts an upper laminated unit and a lower peloidal unit the former is interpreted as a subaerial stromatolite and the latter as an a horizon of a palaeosol comparisons are made with the a horizons of rendzinas and it is concluded that the calcrete crust represents a complete rendzina profile this fossil rendzina contains abundant evidence of a soil fauna in the form of fecal pellets and small burrows

fault linkage patterns and their control on the formation of the petroleum systems of the erlian basin eastern china abstract fault linkage patterns in rift basins are very common while the process of fault linkage may be very short it changes sedimentation patterns before and after linkage and controls the development of half grabens the propagation and growth of boundary faults can be divided into a simple fault propagation pattern and a fault growth linkage pattern based on structural style sedimentation patterns and oil source correlations in the erlian basin three types of grabens and petroleum systems can be identified the abei graben is controlled by a single boundary fault and forms an independent petroleum system the saihantala graben is controlled by several linked faults which also has an independent petroleum system the wuliyasitai depression controlled by two boundary fault segments which results in two petroleum systems as not all half grabens develop one petroleum system they may therefore have two or more systems the relay ramps between fault segments before linkage are the locations of deposition of sands and conglomerates and consequently are the focus areas for stratigraphic lithologic trap exploration

the sedimentary facies of a late bathonian regressive episode the kilmaluag and skudiburgh formations of the great estuarine group inner hebrides scotland the kilmaluag and skudiburgh formations of the bathonian great estuarine group represent a unique palaeoenvironment within the british jurassic the kilmaluag formation is divided into two distinctive facies the clastic facies of n skye comprises calcareous mudstones and shales with subordinate sandstones and argillaceous limestones the depositional setting was one of shallow ephemeral lagoons closed from the sea sublittoral lagoon mudflat and channel environments are identified and fossil faunas indicate low salinity the argillaceous limestone facies of southern skye eigg and muck formed in a similar depositional setting although sandstones are not present alternations of carbonate rocks some dolomitic and calcareous shales probably reflect palaeoclimatic fluctuations between humid and arid periods the overlying skudiburgh formation is interpreted as being alluvial floodplain channel and overbank deposits are identified by the presence of mottled mudstones sands and lensoidal silts syndepositional carbonate nodules are interpreted as calcrete which occasionally coalesced to form extensive hardpan calcrete horizons the vertical facies sequence reflects a late bathonian regression the coastal plain terrestrial environments of the skudiburgh formation were transgressed during the callovian stage an event which ended paralic deposition in the hebridean jurassic

origin of nama basin bitumen seeps petroleum derived from a permian lacustrine source rock traversing southwestern gondwana abstract biodegraded bitumens associated with quartz and calcite veins in the cambrian fish river subgroup sediments of the nama group of southern namibia have a geochemical signature diagnostic for organic matter that was deposited in a saline lacustrine palaeoenvironment in particular they contain abundant gammacerane carotane and 3 methylhopanes while 24 isopropyl cholestanes and dinosteroids are not detectable sealed tube hydrous pyrolysis of asphaltene and polar fractions yielded saturated hydrocarbons amenable to c isotopic analysis and these analyses show unusually low 13 c values these combined characteristics are also present in immature bitumens from the permian irati formation of brazil and a saline lacustrine facies of the whitehill formation in the karoo basin south africa we conclude that the bitumens originated from whitehill equivalent strata of the kalahari basin deposited in what was an extensive saline lacustrine basin in southwestern gondwana during the early permian in southern africa source rocks of the whitehill formation are generally immature for petroleum generation and it is therefore likely that the nama bitumens were expelled by contact metamorphism during emplacement of karoo dolerite sills and dykes in the jurassic

major and trace element geochemistry of bay of bengal sediments implications to provenances and their controlling factors major and trace elements of sediments from a 13 m long piston core sk187 pc33 from the western bay of bengal have been investigated in this study to infer about the changes in provenances and related controlling factors during the last glacial interglacial period factor analysis of these geochemical dataset ascertains dominant role of riverine supply of sediments in regulating the geochemistry of sk187 pc33 sediments the al normalized major k and ti and trace elemental cu and cr ratios of these marine sediments fall within the ranges observed for their major provenances viz ganga brahmaputra and the godavari krishna gk rivers and depth profiles of these ratios showed significant variations with synchronous excursion at around the last glacial maxima lgm implying a change in their provenances with relatively reduced himalayan contribution during this climatic event relatively higher cia and ti ca ratios with lower k al ratios of these sediments during the holocene hint intense chemical weathering in the river basins in response to strengthened monsoon during this period inverse model calculation of al normalized elemental ratios of the sediments estimated an average sediment contribution of 66 13 and 34 13 from the himalayan and the peninsular indian rivers to the core site respectively consistent with the depth profiles of elemental ratios the estimated sediment contributions from the himalayan rivers are observed to decrease by 20 from the himalayan rivers particularly that of the ganga to the studied location during the lgm lowering of sediment supply from the himalaya ganga during the lgm is due to weakening of south west monsoon and reduction in available exposure area for weathering due to extent of glacier cover outcomes of this study underscore the strong linkage between erosion and climate

comparative study between rock eval pyrolysis and biomarkers parameters a case study of ypresian source rocks in central northern tunisia abstract sedimentary rock samples from the ypresian basin in central northern tunisia were analyzed by two well proven organic geochemical methods rock eval re pyrolysis and gas chromatography mass spectrometry gc ms analysis these techniques were uses to obtain independent parameters on organic matter composition its thermal maturity and environment of deposition this study reveals a close concordance between rock eval pyrolysis data and polycyclic biomarkers parameters such as hopanes and steranes re pyrolysis in conjunction with gc ms analysis show that the ypresian basin sediments contain a variable but notable organic rich facies during the ypresian and prove an unequivocal evidence for type ii organic matter which lies dominantly prior to the peak stage of the conventional oil window end of diagenesis beginning of catagenesis the case study from the ypresian basin shows that these methods remain undoubtedly suitable for a good assessment of the petroleum potential of source rocks and rapid geochemical characterization of sedimentary organic matter

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

carbon sulfur iron relationships in sedimentary rocks from southwestern taiwan influence of geochemical environment on greigite and pyrrhotite formation the importance of the magnetic iron sulfide minerals greigite fe3s4 and pyrrhotite fe7s8 is often underappreciated in geochemical studies because they are metastable with respect to pyrite fes2 based on magnetic properties and x ray diffraction analysis previous studies have reported widespread occurrences of these magnetic minerals along with magnetite fe3o4 in two thick plio pleistocene marine sedimentary sequences from southwestern taiwan different stratigraphic zones were classified according to the dominant magnetic mineral assemblages greigite pyrrhotite and magnetite dominated zones greigite and pyrrhotite are intimately associated with fine grained sediments whereas magnetite is more abundant in coarse grained sediments we measured total organic carbon toc total sulfur ts total iron fet 1n hcl extractable iron fea and bulk sediment grain size for different stratigraphic zones in order to understand the factors governing the formation and preservation of the two magnetic iron sulfide minerals the studied sediments have low ts fea weight ratios 0 03 0 2 far below that of pyrite 1 15 which indicates that an excess of reactive iron was available for pyritization observed low ts 0 05 0 27 is attributed to the low organic carbon contents toc 0 25 0 55 which resulted from dilution by rapid terrigenous sedimentation the fine grained sediments also have the highest fet and fea values we suggest that under conditions of low organic carbon provision the high iron activity in the fine grained sediments may have removed reduced sulfur so effectively that pyritization was arrested or retarded which in turn favored preservation of the intermediate magnetic iron sulfides the relative abundances of reactive iron and labile organic carbon appear to have controlled the transformation pathway of amorphous fes into greigite or into pyrrhotite compared to pyrrhotite dominated sediments greigite dominated sediments are finer grained and have higher fea but lower ts we suggest that diagenetic environments with higher supply of reactive iron lower supply of labile organic matter and consequently lower sulfide concentration result in relatively high eh conditions which favor formation of greigite relative to pyrrhotite

terrestrial stromatolites and laminar calcretes a review abstract laminated carbonates are prominent features of subaerial exposure profiles and many types of calcareous soils including calcretes previously much attention was given to differentiating these laminites from marine or lacustrine microbial stromatolites and oncoids however recent research has shown that many subaerial laminated carbonates are biogenically formed mainly but not wholly by microbial activity this paper reviews the criteria for distinguishing terrestrial carbonate laminites from non terrestrial stromatolites and oncoids and for differentiating biogenic from abiogenic terrestrial laminites

biomarker signatures from neoproterozoic early cambrian oil western india abstract the neoproterozoic early cambrian time is the cradle of multicellular eukaryotic life and thereafter metazoan life started populating the planet biomarkers which record the chronicles of biotic events on earth have been investigated using gas chromatography mass spectrometry from a suite of nine oil samples extracted from oil stained sediments and a crude oil of neoproterozoic early cambrian age from bikaner nagaur basin western india the biomarker distribution is characterized by high concentration of both tricyclic terpanes and pentacyclic hopanes the predominance of c 29 regular sterane over c 27 and c 28 steranes indicates green algal contribution and may imply the prominence and diversification of the same algal group the low pristane phytane ratio and occurrence of substantial quantity of gammacerane monomethyl 2 methyl 2 2 4 8 trimethyltridecyl chroman and 1 1 7 8 tetramethyl 1 2 3 4 tetrahydrophenanthrene are indicative of stratified water column as well as anoxic and enhanced salinity condition of the environment of deposition this paper reports for the first time the presence of methyltrimethyltridecyl chromans mttcs from neoproterozoic early cambrian time putative c 19 norsteranes probably indicative of sponge input are recorded in the studied samples and also reported from other infracambrian oils and sediments normal alkanes n c 17 and n c 18 and isoprenoids pristane and phytane are highly depleted in 13 c the overall biomarker distribution and carbon isotope data of oils from bikaner nagaur basin show similarities with those of other infracambrian oils like huqf oils from oman and baykit high oils from eastern siberia

tectonic and climate control of oil shale deposition in the upper cretaceous qingshankou formation songliao basin ne china oil shales were deposited in the songliao basin ne china during the upper cretaceous period representing excellent hydrocarbon source rocks high organic matter om contents a predominance of type i kerogen and a low maturity of om in the oil shales are indicated by bulk geochemical parameters and biomarker data a major contribution of aquatic organisms and minor inputs from terrigenous land plants to om input are indicated by n alkane distribution patterns composition of steroids and organic macerals strongly reducing bottom water conditions during the deposition of the oil shale sequences are indicated by low pristane phytane ratios high c14 aryl isoprenoid contents homohopane distribution patterns and high v ni ratios enhanced salinity stratification with mesosaline and alkaline bottom waters during deposition of the oil shales are indicated by high gammacerane index values low mttc ratios high carotene contents low toc s ratios and high sr ba ratios the stratified water column with anoxic conditions in the bottom water enhanced preservation of om moderate input of detrital minerals during the deposition of the oil shale sequences is reflected by titanium concentrations in this study environmental conditions in the paleo lake leading to om accumulation in the sediments are related to sequence stratigraphy governed by climate and tectonics the first member of the qingshankou formation k2qn1 in the songliao basin containing the oil shale sequence encompasses a third order sequence that can be divided into three system tracts transgressive system tract tst highstand system tract hst and regressive system tract rst enrichment of om changed from low values during tst i to high moderate values during tst ii iii and hst i ii low om enrichment occurs during rst i and rst ii therefore the highest enrichment of om in the sediments is related to stages of mid late tst and early hst

geochemical characterization and depositional environment of source rocks of small fault basin in erlian basin northern china abstract a combined investigation of molecular geochemistry elements and carbon isotopic composition of carbonate distribution was carried out on the early cretaceous mudstones of the tengger formation in the erlian basin northern china to define source rock geochemical characteristics depositional environment and tectonic setting of small faulted basin the biomarkers of mudstone extracts are characterized by short to middle chain n alkanes high cpi values 1 12 a wide range of pr ph 0 4 1 94 relatively high concentrations of c 29 sterane and the presence of relatively low tricyclic terpanes and low gammacerane index values 0 01 0 25 which is consistent with a relatively oxic to anoxic depositional environment of fresh to brackish water conditions with a major contribution of terrigenous organic matter input and a low contribution of aquatic algal bacterial organic matter the oxic to anoxic depositional environment of small fault basins and a fresh and brackish water conditions are also confirmed by reduced sulphur organic carbon ratio and element distribution in these small fault basins the cross plots of 13 c carb and toc show that productivity has an obvious control on source rock development the differences in tectonic settings cause variations in productivity redox conditions and terrigenous organic matter input which account for the distinctly different geochemical characteristics and depositional environment of source rocks in small fault basins

origin of an unusual heavy oil from the baiyinchagan depression erlian basin northern china abstract a detailed organic geochemical analysis of six oil samples from the baiyinchagan depression in the erlian basin northern china was carried out in order to evaluate their origin the oils are reservoired at a very shallow depth 223 560 m subsurface and their chemical and physical properties vary greatly ranging from normal to extremely heavy oil the preservation of non biodegraded oil in such a shallow reservoir is possibly related with palaeo pasteurization of the reservoir before uplift maturity difference is not the primary control on the chemical and physical properties of the oils and there is considerable geochemical evidence to suggest the additional influence of in reservoir post accumulation processes such as biodegradation water washing and possibly evaporation whereas some oils appear to be less affected others are moderately biodegraded up to level 4 on the peters and moldowan 1993 scale with sterane distributions largely unaffected and 25 norhopanes undetected contrary to classical biodegradation the unusual heavy oil shows little evidence of biodegradation from aliphatic components water washing is suggested to be the primary process leading to its formation since the severe alteration of soluble aromatic hydrocarbons is observed in addition since the oils have been uplifted significantly after accumulation evaporation and or leakage to modify oil compositions cannot be ruled out

tetrahymanol its widespread occurrence and geochemical significance abstract the occurrence of tetrahymanol gammaceran 3 ol in sediments from various marine depositional environments such as the santa monica basin and palos verdes shelf southern california bight the santa barbara basin off the northern california borderland the atlantic shelf slope and rise and the antarctic region as well as in bacterial algal mats from the santa barbara basin and baja california together with its detection in sediments from the peru upwelling region odp leg 112 and baffin bay odp leg 105 suggests that tetrahymanol occurs ubiquitously in marine samples tetrahymanol is the only known likely biological precursor of gammacerane which is found in many petroleums and shales the common occurrence of tetrahymanol in marine environments implies that primitive organisms similar to tetrahymena or organisms other than tetrahymena other protozoa bacteria are also likely to contain this compound its isomer diplopterol has also been detected in several sediment sections

carbon sulfur iron relationships and δ13c of organic matter for late albian sedimentary rocks from the north atlantic ocean paleoceanographic implications abstract cores from six deep sea drilling project sites 367 369 137 386 387 and 603 of the late albian north atlantic ocean were investigated for organic carbon content 13c values of the kerogens maceral composition of the organic matter c s ratios fe toc s relationships and framboidal pyrite size distribution in order to evaluate processes that led to the accumulation of organic matter rich black shale deposits the results show a clear separation of the albian north atlantic into an anoxic eastern part and a mostly oxic western part the eastern north atlantic is dominated by organic matter rich deposits sulfate reduction occurred in an oxygen free water column and resulted in characteristic c s ratios fe toc s relationships and framboidal pyrite size distribution patterns elevated productivity anoxia and high sedimentation rates supported the formation of black shale deposits for most of the western and central parts organic matter sedimentation took place through an oxygenated water column the accumulated organic matter is dominantly of terrigenous origin the deposition of marine derived organic matter was most likely controlled by productivity paleobathymetry and low sedimentation rates

biomarkers as environmental indicators in a carbonate complex example from the middle to upper devonian holy cross mountains poland abstract autochthonous biomarker distributions were studied in an array of different subfacies of a devonian carbonate complex represented in platform reef and off platform shelf basinal systems it revealed that biomarkers are sensitive indicators of depositional environments and may serve to refine palaeoenvironmental interpretations of carbonate complexes based on classical sedimentological facies analyses the contrasting biomarker composition of the carbonate platform and reef complex versus shelf basin deposits is here interpreted as the effect of both more diverse biotic sources of a primary organic matter in the former environments highly scattered results of sterane distribution and contrasting styles of decay and bacterial reworking of the primary biomass peritidal dolostones deposited under anoxic to suboxic conditions and with scarce sedimentological evidence of elevated salinity reveal the highest potential of organic matter preservation among other platform reefal facies their biomarker composition includes several compounds indicating hypersaline conditions and anoxia whereas others in particular gammacerane indicate that the water column was stratified during sedimentation this observation constrains environmental interpretation of these deposits pointing to shallow subtidal lagoons with elevated salinity and low oxygen near bottom waters most probably originating from a salinity controlled stratification of the water column biomarkers diagnostic of green sulphur bacteria were found in both peritidal lagoonal dolostones and shelf basinal facies this indicates the existence of photic zone anoxia in the latter environment thus suggesting a shallow position of the redoxcline the frasnian famennian mass extinction event s apparently had no impact on the biomarker distribution in the shelf basinal system continuous across the stage boundary

magnetotelluric and seismic evidences for crust mantle heterogeneities abstract based on published results an attempt has been made to correlate the electrical conductivities and seismic velocities obtained from magnetotelluric mt sounding geomagnetic depth sounding gds earthquakes deep nuclear explosions and dispersion of surface waves the correlation profile extends from the scandinavian shield to mariana islands and passes through parts of europe the atlantic ocean canada the u s a the pacific ocean and hawaiian islands inverted mt gds and seismic data are plotted against depth on a regional scale to obtain geoelectric and seismic sections regional variation of the depth of the moho is shown large scale lateral crust mantle heterogeneities along with the tectonically active zones are broadly reflected in these sections hcls high conductivity layers and lvzs low velocity zones are delineated phase transition of silicates may explain the electrical conductivity and seismic velocity changes at a depth of about 400 km the western u s a basin and range province colorado plateau near the east pacific rise reveals significant lateral variations along with a few partial melt pockets heterogeneities extend up to 1000 km a tentative temperature section has been constructed based on the electrical conductivities of the probable components

organic matter and trace element rich sapropels and black shales a geochemical comparison a distinct pliocene eastern mediterranean sapropel i 282 recovered from three ocean drilling program odp leg 160 sites has been investigated for its organic and inorganic composition this sapropel is characterized by high organic carbon corg and trace element contents and the presence of isorenieratene derivatives the latter suggests that the base of the photic zone was sulphidic during formation of the sapropel combined with evidence of bottom water anoxia preservation of laminae high redox sensitive trace element contents and the abundance and isotopic composition of pyrite this leads to the tentative conclusion that almost the entire water column may have been anoxic this anoxia resulted from high productivity and not from stagnation because an approximation of the trace element budget during sapropel formation shows that water exchange with the western mediterranean is needed entire water column anoxia has been suggested earlier for several black shales with regard to the depositional environment and the corg content however only the cenomanian turonian boundary event ctbe black shales appear to be comparable to this sapropel the proposed trace element removal mechanism of scavenging and co precipitation in an anoxic water column is thought to be similar for both types of deposits the ultimate trace element source for the sapropel however is seawater whereas it is hydrothermal and fluvial input for ctbe black shales because they have a larger temporal and spatial distribution nonetheless the corg rich eastern mediterranean pliocene sapropel discussed here may be considered to be a younger analogue of ctbe black shales

podogenic columnar calcite from the oolite group lower carboniferous south wales abstract calcrete palaeosols in the oolite group have microspar hardpan layers overlying clay rich nodular layers which in turn overlie the degraded host oolite within and immediately below hardpan layers there are extensive sheet like and fan developments of columnar calcite with individual crystals up to 30 cm long crystals range from those with straight extinction and normal growth zonation through feathery crystals to those showing sweeping extinction the calcretes accumulated within a seasonal climate with hardpan accumulation probably occurring through evaporation during the dry season the columnar calcite precipitated from more dilute solutions with maximum growth probably occurring during the wet season precipitation may have been partly or wholly bacterially mediated or induced by the reduction in p co 2 of fluids as they migrated out of the extremely restricted microporosity of the hardpan columnar fabrics reflect low supersaturations relative to those at which the hardpan accreted inhibition of crystal nucleation and of growth on x axis parallel faces and an excess of co 2 2 availability over ca 2 growth and nucleation may have been inhibited by the presence of particular organic compounds or clays the range in crystal form is related to the degree of poisoning of crystal growth faces by organic compounds

organic geochemical evaluation of cretaceous shale samples from the orange basin south africa abstract organic geochemical evaluation of thirty two aptian to campanian shale samples from seven wells drilled on the shelf of the orange basin southwestern atlantic margin was carried out in order to determine their origin depositional environment thermal maturity and hydrocarbon potential the shale samples selected to represent highstand lowstand and transgressive systems tracts were analysed by rock eval pyrolysis for total organic c characteristics and by gas chromatography gc and gas chromatography mass spectrometry gc ms for n alkanes aliphatic isoprenoid hydrocarbons and biomarkers steranes hopanes and tricylic terpanes for most of the shale samples rock eval data hydrogen hi and oxygen index oi point to mainly type iii terrigenous organic matter only a few samples of turonian age reveal a higher proportion of marine organic matter being classified as type ii iii or type ii biomarker parameters suggest that the samples are deposited under suboxic to oxic environmental conditions rock eval data and biomarker maturity parameters assign for most of the samples a maturity level at the beginning of the oil window with some more mature samples of aptian albian and cenomanian age the hydrocarbon generation potential is low for most of the shelf shales as indicated by the s2 s3 ratio and hi values exceptions are some samples of turonian and aptian age

evidence for euphotic zone anoxia during the deposition of aptian source rocks based on aryl isoprenoids in petroleum sergipe alagoas basin northeastern brazil organic geochemistry laboratory chemistry department college of natural sciences federal university of piaui campus minister petronio portella teresina pi 64049 550

organic carbon burial rates and carbon and sulfur relationships in coastal sediments of the southern baltic sea abstract organic c burial rates and c s relationships were investigated in the holocene sediment sequences of 3 shallow polymictic coastal lagoons in the southern baltic sea to better understand the biogeochemical cycling of c and s in these environmental systems the results show that these lagoons may have a considerable influence on the environmental status of the southern baltic sea area in having the potential to act as a temporary sink or source for heavy metals high organic c accumulation rates corg ar can be observed in the sediments due to a high organic matter supply from land and a high productivity of the water bodies as a result of eutrophication however organic c burial does not increase as a result of increasing sediment accumulation rates sar even when high sedimentation rates do occur there appears to be a thorough recycling and resuspension of the sediment enhancing the biological decay of organic matter before burial or the removal of organic matter from the system by transport that is why high sar in the coastal lagoons do not enhance pyrite formation and thereby permanent fixing of heavy metals in the sediments to the extent that could be expected from their magnitude initially there is a high potential for a temporary binding of heavy metals but the latter are likely to be subject to mobilization and redistribution within the sediments and the water column the patterns of burial of organic and mineral matter are different from those observed in the present day baltic proper implying possible important links in deposition between the central and coastal areas of the baltic sea and implications for c cycling in the ecosystem of the baltic sea