organic geochemical characteristics and generating potential of source rocks from the lower middle jurassic coal bearing strata in the east junggar basin nw china abstract the junggar basin located in nw china is a large intracontinental superimposed basin samples were collected from the lower middle jurassic coal bearing strata of the eastern junggar basin and include mudstones carbargilites and coal the origin of organic matter thermal maturity paleoenvironment of sediment deposition and hydrocarbon potential of drill core samples was investigated organic geochemical analysis performed on 65 source rock samples indicates a wide range of toc values from 0 81 wt to 81 06 wt this study combined sedimentology biomarker organic petrography and stable carbon isotopic composition of kerogen and extracts analysis demonstrating the organic matter of the source rocks is derived from terrestrial higher plants with a minor contribution of aquatic algae and microbes rock eval data elemental composition of kerogen and odd over even normal alkane distribution reveal immaturity to low maturity with a humic type organic matter the source rocks were deposited in a freshwater oxic to sub oxic environment indicated by high pr ph ratios a predominance of c29 steranes low tricyclic terpanes and a low gammacerane index high dia regular c29 sterane ratios and moderate to high c29 c30 hopane ratios found in most samples are related to the presence of clay minerals based on the following parameters h c vs o c toc s1 s2 hydrogen index saturated hydrocarbons aromatic hydrocarbons and chloroform a we concluded that the samples collected from organic rich coal bearing strata may yield not only gas but also have the capability to generate and release liquid hydrocarbons

mesozoic rift basins of yemen abstract this special issue is the first compilation and review of the stratigraphy and basin evolution of the mesozoic petroleum basins of yemen the volume arises from an international symposium on the sedimentation and tectonics of rift basins of the red sea gulf of aden area held at the university of sana a in september 1995 papers relating to the cenozoic rifting of the gulf of aden red sea and gulf of suez are to be published shortly b h purser and d w j bosence sedimentation and techtonics of rift basins the red sea gulf of aden chapman and hall london in press eight papers within this issue focus on basins within the interior of the country and the margins of the gulf of aden indian ocean the papers cover reviews of the developing stratigraphic concepts for these basins outcrop studies and subsurface studies of recently explored areas by geoscientists from the u k oil industry and from u k lebanese and yemeni universities

intersector element partitioning in tourmaline a potentially powerful single crystal thermometer hourglass sector zoning and related polar overgrowths are common features of metamorphic tourmaline developing as a result of variations in element preference on the different growth surfaces for sector zoned crystals three domains are present for each growth zone c c and a with compositional differences most distinct for ca and ti and among c and c sectors intersector differences vary commonly showing decreasing fractionation from core to rim attributed to increasing metamorphic grade here we show that intersector element partitioning is temperature dependent and derive empirical geothermometers based on c c and c a partitioning of ca and ti these thermometers are applicable over a range of temperatures and bulk rock compositions intersector partitioning is not affected by re equilibration and records and preserves complete t histories of individual tourmaline grains from prograde to peak and on to retrograde growth information on element mobility is preserved by tourmaline composition because intersector partitioning is independent of element concentration these factors make intersector partitioning an ideal tool to elucidate the thermal history of tourmaline grains and thus their host environment and tourmaline s refractory nature preserves these signatures even into the sedimentary record

madbi biyadh qishn petroleum system in the onshore masila basin of the eastern yemen abstract the masila basin is one several onshore mesozoic basins in yemen however a full petroleum system with its essential elements and processes has not been assigned yet in this study one petroleum system in the masila basin was identified and named madbi biyadh qishn petroleum system an extensive overview study showed that the main source and reservoir rocks in the masila basin are the upper jurassic madbi shales and lower cretaceous biyadh qishn sandstones respectively hence it appears that the most important effective petroleum system of the masila basin becomes the madbi biyadh qishn petroleum system organic rich shales of the upper part of the madbi formation deposited during the upper jurassic constitute the main source rock of the crude oils in the basin these shales contain high total organic carbon content toc 2 0 wt and predominantly algal type ii with minor type i kerogen the madbi shales are mature and at the present time are within the oil window with determined vitrinite reflectance values in the range of 0 53 0 91 ro the biyadh qishn sandstones are the main reservoir and were deposited in braided river channels shoreface and shallow marine environments and consist of fine to coarse grained moderate to well sorted grains seal rocks are cretaceous limestone and shales of the qishn and harshiyat formations and tertiary shales overburden rocks include the cretaceous rocks and the tertiary sediments deposited simultaneously with development of the traps during oligocene middle miocene time burial thermal histories models demonstrate that hydrocarbon generation from the madbi shales commenced in the late cretaceous and maximum rates of hydrocarbon expulsion occurred during the early tertiary geochemical oil source rock correlation studies showed that regional distribution of the oil fields almost overlap with the previously constructed pod of active madbi shales indicating that oil migrated from the active madbi source rock to trapping sites via vertical migration pathways through faults as a result of tertiary rifting during oligocene middle miocene time

the origin and mode of emplacement of lujavrites in the ilimaussaq alkaline complex south greenland abstract lujavrites are rare meso to melanocratic agpaitic nepheline syenites that are characterized by elevated contents of elements such as li be zr ree nb th and u they are the most evolved members of the three large composite agpaitic complexes lovozero kola peninsula russia pilansberg south africa and ilimaussaq south greenland and are inferred to stem from the same deep fractionating magma sources that fed the earlier members of the complexes the composition of the melts that evolved into lujavrites is however not well known the agpaitic part of the ilimaussaq complex is divided into a roof series a floor series of cumulates and an intermediate series of lujavrites sandwiched between the two in the traditional view the lujavrites formed from residual melts left between the downward crystallizing roof series and the floor cumulates new field observations and geochemical data suggest that the floor cumulates and the main mass of lujavrites constituted a separate intrusive phase which was emplaced into the already consolidated roof series rocks largely by piecemeal stoping studies of the contact facies of the floor cumulates indicate that the initial magma of the floor cumulate lujavrite sequence was peralkaline nepheline syenitic with enhanced contents of zr hf hree y nb ta f ba and sr subsequent crystallization in a closed system resulted in the formation of the floor cumulates and lujavrites chemical analyses of dykes within and outside the complex represent stages in the magmatic evolution of the agpaitic rocks

characterization of tar like material and producible oil in misoa c2 and c3 reservoir sands of the area 2 south ceuta field venezuela abstract here we characterized asphaltic oil occurrences in the misoa c2 and c3 reservoirs within area 2 south of the ceuta field lake maracaibo basin nw venezuela to perform the geochemical and petrological characterization of the c2 and c3 sub units which cover an interval in which tar like material was detected we analyzed core 18 and cutting 123 samples using the rock eval 6 technique in reservoir mode samples were studied under fluorescence light and scanning electron microscopy sem showing the presence of two charges of oils and the relationships within silica cements and clay minerals to evaluate vertical inter reservoir communication and lateral intra reservoir continuity we also studied 12 oil samples from wells in area 2 south biomarkers and isotopic signatures were examined using gas chromatography mass spectrometry gc ms and isotope ratio mass spectrometry irms the results suggest that oil and core extracts belongs to a single family derived from two pulses of hydrocarbon generation from the la luna source rock which was deposited in a marine reducing environment the oil samples are a mixture of a paleobiodegraded oil charge and a later fresh more mature oil recharge the geochemical analyses also evidence that the formation of heavy oil tar zones can be related to biodegradation and in reservoir oil mixing though other formation mechanisms for the tar are also feasible finally the gc fingerprints of the oils are indicative of lateral reservoir continuities across the f 1 and f 2 faults and vertical communication between the misoa c2 and c3 sub units in area 2 south suggesting that tar occurrences do not act as permeability barriers within the two reservoirs studied

the mineralogical diversity of alkaline igneous rocks critical factors for the transition from miaskitic to agpaitic phase assemblages geochemically the large family of alkaline plutonic rocks both qtz undersaturated and oversaturated compositions can be subdivided into metaluminous na 2 o k 2 o al 2 o 3 types in this paper we discuss two important aspects of the mineralogical evolution of such rocks with respect to their fe mg phases a major mineralogical transition observed is the precipitation of arfvedsonite or aegirine instead of fayalite or magnetite ilmenite the relative stability of these phases is controlled by oxygen fugacity and na activity in the crystallizing melts if na activity in the melt is high enough arfvedsonite aegirine form a common assemblage in peralkaline rocks under both reduced and oxidized conditions major mineralogical differences within this rock group exist with respect to their high field strength element hfse rich minerals most syenitic rocks known as miaskites contain zircon titanite or ilmenite as hfse rich minerals whereas in agpaites complex na k ca ti zr silicates incorporate the hfse similarly only a small group of peralkaline granites are found to lack zircon titanite or ilmenite but instead contain na k ca ti zr silicates here we present a detailed phase petrological analysis of the chemical parameters na 2 o cao k 2 o that influence the transition from miaskitic to agpaitic rocks based on the occurrence of ti and zr minerals several transitional mineral assemblages are identified and two major evolution trends for agpaites are distinguished a high ca trend which is exemplified by the alkaline rocks of the kola province russia and a ca depletion trend which is displayed by the alkaline rocks of the gardar province south greenland both trends show significant na enrichment during magmatic evolution high ca agpaites evolve from nephelinitic parental melts that did not crystallize large amounts of plagioclase in contrast agpaites showing ca depletion originate by extensive fractionation of plagioclase from basaltic parental melts in some peralkaline granites evolutionary trends are observed that culminate in agpaite like hfse mineral associations in the most evolved rocks

oil generation characteristics of mesozoic syn rift madbi source rock in the masila basin eastern yemen new insights from kerogen pyrolysis and bulk kinetic modelling abstract organic rich shale layer is present within the syn rift madbi formation of the masila basin representing excellent oil source rock twenty five representative immature to very early mature source rock samples from the upper jurassic madbi shale sequences were investigated using bulk and quantitative pyrolysis techniques the analytical program included toc pyrolysis sra pyrolysis gc bulk kinetics and kerogen microscopy the results were used to characterize the kerogen composition and type of petroleum generated during thermal maturation from madbi source rock and to clarify the variability of the organic matter and their effect on the timing of petroleum generation pyrolysis data identi ed two major organic facies with different petroleum generation characteristics type ii kerogen with hi values of 400 mg hc g toc type ii iii facies with hi values bulk kinetic analysis on madbi shale samples indicate that the type ii facies mostly derived from a homogenous organic matter spans relatively narrow distribution of activation energy 50 54 kcal mol and predicted petroleum formation temperature is very different with onset tr 10 temperatures of 125 c geological tmax 138 c in contrast the type ii iii facies reveals a relatively broad distribution of activation energies 40 kcal mol to 62 kcal mol that are directly related to the heterogeneity in the organic matter onset tr 10 temperatures of 106 c geological tmax 139 c the bulk kinetic analysis also suggested that the peak generation temperatures geological tmax are variable and ranging from 135 c to 142 c reaching a signi cant transformation ratio 50 tr therefore the madbi source rock potential could have be generated and expelled mature oils in the masila basin

δ13c compositions of saturate and aromatic fractions of lacustrine oils and bitumens evidence for water column stratification abstract saturate fractions of oils and source rocks are generally depleted in 13 c relative to the aromatic fraction the isotopic difference between these two fractions aro sat is largest typically in lacustrine oils and bitumens and smallest in marine samples depletions of 13 c in saturate fractions in samples from three lacustrine basins china argentina and u s a correlate strongly with hopane abundance extremely 13 c depleted hopanes have been documented in ancient and modern lacustrine settings and are explained by input from methanotrophic bacteria as these bacteria thrive at the chemocline of stratified lakes extremely 13 c depleted hopanes in geologic samples is evidence for paleostratification comparatively low aro sat values in marine samples are related to abundant sulfate in marine environments since sulfate reducers out compete methanogens for metabolic intermediates and attenuate the methane cycle the strong positive correlation of quantitative hopane abundance with the 13 c depletion in saturate fractions of lacustrine samples provides circumstantial evidence for biogenic input from methanotrophic bacteria and for stratified water columns during source rock deposition further this observation explains why the sofer plot effectively differentiates stratified lacustrine samples from open marine and non stratified lacustrine samples the wide distribution of our sample set suggests that this is a global phenomenon

source rock characterization and oil generating potential of the jurassic madbi formation onshore east shabowah oilfields republic of yemen abstract the hydrocarbon source rock potential of shales from the jurassic madbi formation was evaluated using organic geochemistry rock eval pyrolysis toc and bitumen extraction and organic petrology very good source rock potential is suggested by high values of total organic carbon content toc 2 0 wt and high extractable organic matter content and hydrocarbon yields 11 000 and 6000 ppm respectively the madbi formation samples have high hydrogen index hi and low oxygen index oi values most of the samples in the study area are thermally mature and contain oil prone type i and type ii kerogen vitrinite reflectance ro values for the madbi shale samples were measured from 0 74 to 0 89 tmax values range from 430 to 438 c which are in reasonably good agreement with vitrinite reflectance data reveal that the madbi shales are at the early to peak mature stage on the basis of biomarker maturity parameters these shales are thermally mature shales of the madbi formation contain abundant hydrogen rich kerogen liptinite up to 55 and therefore good oil generating potential is anticipated this is supported by high hydrogen indices hi of up to 400 mg hc g toc and early to peak mature oil window range

biological markers and carbon isotope composition of organic matter in the upper cretaceous coals and carbonaceous shale succession jiza qamar basin yemen origin type and preservation abstract bituminous coals and carbonaceous shales located in the jiza qamar basin on the eastern yemen were analysed based on a combined investigation of organic geochemistry and petrology to define the palaeodepositional environment condition organic matter inputs and their thermal maturity carbon isotope compositions and various biomarkers were performed on coals and carbonaceous shales within the upper cretaceous mukalla formation in the jiza qamar basin the 13 c values range from 29 2 to 24 5 with average values around 26 7 whereas the organic carbon contents in most sediment samples are consistently high 3 indicating that the organic matter in the mukalla coal and carbonaceous shale sediments has a predominantly terrigenous origin with slightly marine influence during burial this has also been identified from kerogen microscopy which is characterized by dominance of vitrinite and liptinite organic matter the investigated biomarkers indicated that the mukalla coals and carbonaceous shales contain high contribution of land plants with a minor aquatic organic matter input that was deposited in a fluvial to deltaic environments and preserved under relatively oxic conditions this has been achieved from acyclic isoprenoids terpane and sterane biomarkers of a saturated hydrocarbon and dibenzothiophene alkylnaphthalene and methylphenanthrene biomarkers of an aromatic hydrocarbon based on the analysed biomarker thermal maturity indicators it may be deduced that the mukalla coals and carbonaceous shales in the jiza qamar basin have entered an early mature to mature stages for hydrocarbon generation this is also supported by vitrinite reflectance values of 0 63 0 83 ro indicative that these sediments have reached oil window maturity

repeat ridge jumps and microcontinent separation insights from ne arabian sea abstract microcontinents separate due to ridge jumps associate either asymmetric sea floor spreading or plume ridge interactions india separated from seychelles at 64 ma by asymmetric sea floor spreading initially when the spreading centre in the mascarene basin jumped towards the indian sub continent between magnetic chrons c29 and c28 the subsequent tectonics is difficult to comprehend since laxmi ridge another microcontinent formed during the later phase most of the studies considered the laxmi ridge as a sliver others considered it to be oceanic crust high resolution deep 25 km seismic data reveals that i the ridge possesses 15 km deep sea ward dipping reflector sdr packages ii normal faulted rift valleys devoid of syn rift sedimentary packages and iii axial magma chambers 5 7 km beneath the ridge top additionally from 2d forward gravity models we deduce that the ridge most possibly comprises of high density oceanic crust we conclude the laxmi ridge to be indeed composed of oceanic crust and a fossil spreading centre we thus identified the ridge jumps and their relation to the seychelles microcontinent separation previous numerical models suggest that the time required for a ridge jump is controlled by magmatic heating spreading rate at the ridge and plate ages for repeated ridge jumps the additional factor is the dynamic relation between the plume and lithosphere in terms of melt transfer and heating we find that the medium spreading rates and high magmatic heating due to the reunion plume and young plates favoured rapid and repeated ridge jumps towards the plume

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

geochemistry and organic petrology study of kimmeridgian organic rich shales in the marib shabowah basin yemen origin and implication for depositional environments and oil generation potential kimmeridgian organic rich shales of the madbi formation from the marib shabowah basin in western yemen were analysed to evaluate the type of organic matter origin and depositional environments as well as their oil generation potential results of the current study establishes the organic geochemical characteristics of the kimmeridgian organic rich shales and identifies the kerogen type based on their organic petrographic characteristics as observed under reflected white light and blue light excitation kerogen microscopy shows that the kimmeridgian organic rich shales contain a large amount of organic matter consisting predominantly of yellow fluorescing alginite and amorphous organic matter with marine microfossils e g dinoflagellate cysts and micro foraminiferal linings terrigenous organic matters e g vitrinite spores and pollen are also present in low quantities the high contributions of marine organic matter with minor terrigenous organic matter are also confirmed by carbon isotopic values the organic richness of the kimmeridgian shales is mainly due to good preservation under suboxic to relatively anoxic conditions as indicated by the percent of numerous pyritized fragments associated with the organic matter the biomarker parameters obtained from mass spectrometer data on m z 191 and m z 217 also indicate that these organic rich shales contain mixed organic matter that were deposited in a marine environment and preserved under suboxic to relatively anoxic conditions the kimmeridgian organic rich shales thus have high oil and low gas generation potential due to oil window maturities and the nature of the organic matter with high content of hydrogen rich type ii and mixed type ii iii kerogens with minor contributions of type iii kerogen

rare earth elements in apatite as a monitor of magmatic and metasomatic processes the ilimaussaq complex south greenland abstract textural and compositional variations of apatite from the plutonic ilimaussaq complex in south greenland and its surrounding country rocks track magmatic and metasomatic processes detailed back scattered electron bse imaging reveals various types of apatite textures including i growth zonation concentric oscillatory as well as sector zonation formed during magmatic differentiation ii resorption and overgrowth textures due to fluid melt induced metasomatic overprint of precursor apatite and iii replacement textures indicating the destabilization of apatite in favor of monazite in the least evolved rocks of the ilimaussaq complex apatite incorporates rare earth elements and y rey mainly via the coupled substitution ca 2 p 5 rey 3 si 4 in the more evolved peralkaline rocks and in metasomatically overprinted rocks however the coupled substitution 2 ca 2 rey 3 na becomes increasingly relevant and apatite incorporates successively more lree compared to hree as shown by increasing la gd n and gd yb n ratios similarly at the contact between the ilimaussaq rocks and the granitic country rocks the metasomatic effect of the emplacement of the ilimaussaq melts is preserved in partly resorbed precursor apatite which is overgrown by rey enriched apatite with higher la gd n and gd yb n ratios compared to apatite from granites more distant from the contact this study shows that apatite textures and compositions are suitable to track both primary magmatic and later fluid present metasomatic processes the incorporation of rey in apatite is not only dependent on the amount of rey present but also depends largely on na activity in the apatite precipitating melts and fluids

near n s paleo extension in the western deccan region india does it link strike slip tectonics with india seychelles rifting this is the first detailed report and analyses of deformation from the w part of the deccan large igneous province dlip maharashtra india this deformation related to the india seychelles rifting during late cretaceous early paleocene was studied and the paleostress tensors were deduced near n s trending shear zones lineaments and faults were already reported without significant detail an e w extension was envisaged by the previous workers to explain the india seychelles rift at 64 ma the direction of extension however does not match with their n s brittle shear zones and also those faults sub vertical ne sw nw se and few n s we report and emphasize in this work slickenside bearing fault planes brittle shear zones and extension fractures in meso scale enabled us to estimate the paleostress tensors directions and relative magnitudes the field study was complemented by remote sensing lineament analyses to map dykes and shear zones dykes emplaced along pre existing n s to ne sw nw se shears fractures this information was used to derive regional paleostress trends a nw se ne sw minimum compressive stress in the oldest kalsubai subgroup and a n s direction for the younger lonavala wai and salsette subgroups were deciphered thus a nw ne to n s extension is put forward that refutes the popular view of e w india seychelles extension paleostress analyses indicate that this is an oblique rifted margin field criteria suggest only ne sw and nw se with some n s strike slip faults brittle shear zones we refer this deformation zone as the western deccan strike slip zone wdsz the observed deformation was matched with offshore tectonics deciphered mainly from faults interpreted on seismic profiles and from magnetic seafloor spreading anomalies these geophysical findings too indicate oblique rifting in this part of the w indian passive margin we argue that the seychelles microcontinent separated from india only after much of the dlip erupted further studies of magma rich passive margins with respect to timing and architecture of deformation and emplacement of volcanics are required

early generation characteristics of a sulfur rich monterey kerogen this paper documents the critical role of organic sulfur in the early formation of bitumen and oil from a sulfur rich kerogen from the miocene monterey formation in california monterey kerogen commonly contains abundant chemically bound sulfur 8 14 wt which appears responsible for early low temperature generation of heavy sulfur rich petroleum due to the lower energy required to break carbon sulfur bonds compared to carbon carbon bonds hydrous pyrolysis was used to simulate the natural generation of petroleum from a sulfur rich type ii kerogen from the phosphatic member of the monterey shale the amount and distribution of sulfur in the kerogen bitumen and expelled oil generated at various temperatures indicate that 1 initial bitumen and oil generation is directly related to cleavage of weak sulfur linkages and 2 most of the expelled oil is formed by decomposition of bitumen and not directly from the kerogen finally comparison of hydrous pyrolysis results with other type ii kerogens suggests that the temperature of peak bitumen generation is inversely related to the heteroatom content primarily sulfur of the kerogen low temperature bitumen generation is an important exploration concept because kerogen rich in sulfur can generate producible oil at thermal maturities significantly below conventionally accepted values furthermore established relationships between thermal maturity sulfur content and other oil properties such as api gravity can be used to rank exploration prospects

petroleum systems of the upper magdalena valley colombia abstract in the upper magdalena valley colombia four petroleum systems were identified two petroleum systems are located in the girardot sub basin and the other two in the neiva sub basin limestones laterally changing to shales of the lower part of the villeta gp deposited during albian and turonian marine flooding events constitutes the main source rocks of the oil families these rocks contain 1 4 toc and type ii kerogen the littoral quartz arenites of the caballos albian and monserrate maastrichtian fms are the main reservoir rocks seal rocks are cretaceous and paleocene shales overburden includes the cretaceous rocks and the tertiary molasse deposited simultaneously with development of two opposite verging thrust systems during cenozoic time these deformation events were responsible for trap creation except for the villarrica area where the source rock reached maturity during the paleocene generation occurred during miocene two oil families are identified each in both sub basins one derived from a clay rich source and the second from a carbonate rich source rock lithofacies of the lower part of villeta gp geochemical source rock to oil correlations are demonstrated for the three of the petroleum systems up dip lateral migration distances are relatively short and faults served as vertical migration pathways a huge amount of oil was probably degraded at surface as a result of miocene deformation and erosion

rifted margin source rock deposition a carbon isotope and biomarker study of a west african lower cretaceous lacustrine section lower cretaceous passive margin sections penetrated in wells peripheral to the deep basinal development of pre salt sediments of the liawenda ponta vermelha troughs in the lower congo coastal basin revealed sustained source potential kerogen type kinetic ea a and carbon isotopic data plus rock extract biomarker signatures confirmed large systematic organofacies variations within these rift phase sediments an inverse correlation between 25 28 30 trisnorhopane and gammacerane abundances suggested three major depositional regimes reflecting salinity and water depth control 13c depleted basal sediments showing strong gammacerane 4 methyl sterane signatures were segregated by a major isotopic excursion this event represented the transition between saline playa lake to deeper water stratified conditions supporting a high level of anoxia for these intermediate sediments sterane and tricyclic diterpane abundances plus sterane hopane ratios had marine connotations and could be interpreted as the result of intermittent marine incursions fore shadowing irreversible oceanic ingression a resurgence of gammacerane abundance in the uppermost sediments typified littoral shallow marine depositional conditions recognition of a possible non ubiquity in lacustrine depositional conditions during the opening of a rifted margin provides further insight into the complexity and attendant controls on hydrocarbon generation in such habitats

geochemical characteristics of the triassic chang 7 lacustrine source rocks ordos basin china implications for paleoenvironment petroleum potential and tight oil occurrence abstract the fact that high quality lacustrine source rocks generally shale and mudstone control the formation and distribution of conventional and unconventional oil and gas reservoirs in lacustrine basins has been well accepted in petroleum exploration and exploitation taking the chang 7 lacustrine source rocks in the ordos basin as an example several points having been reached are as follows 1 the chang 7 source rocks possess an excellent source rock potential and the shales hold a better potential than the mudstones 2 the paleoenvironments of the chang 7 source rocks were sub reducing to sub oxidizing conditions and fresh and brackish water depositional environments with a maximum water depth of 150 m the organic matter origins of the source rocks are mainly plankton algae bacteria and other aquatic microorganisms 3 the beginning time of the oil generation of the chang 7 source rocks is at 165 ma and the peak oil generation occurred during 115 95 ma the cumulative amounts of oil generation are up to 4711 103 t km2 and the ratios of peak generation amounts to cumulative generation amounts are 50 the beginning timing and peak generation timing of the shales are earlier than those of the mudstones respectively and the cumulative oil generation amount of the shales is higher than that of the mudstones indicating a better oil generation potential of the shales 4 due to the more remained oil possessed in the shales the hydrocarbon expulsion threshold of the chang 7 shales 2560 m is deeper than that of the chang 7 mudstones 2080 m 5 the occurrences of the chang 8 6 tight oils are predominantly controlled by the outer boundary of the chang 7 source rocks distribution while the transition areas between thickness toc and ro high value centers are the accumulation and enrichment zones the chang 7 shales controlled the occurrence of the chang 8 tight oil reservoirs and the chang 7 mudstones controlled the occurrence of the chang 7 and chang 6 tight oil reservoirs

arrested kinetic li isotope fractionation at the margin of the ilimaussaq complex south greenland evidence for open system processes during final cooling of peralkaline igneous rocks li contents li and isotopic composition 7 li of mafic minerals mainly amphibole and clinopyroxene from the alkaline to peralkaline ilimaussaq plutonic complex south greenland track the behavior of li and its isotopes during magmatic differentiation and final cooling of an alkaline igneous system li in amphibole increase from b10 ppm in caamphiboles of the least differentiated unit to n3000 ppm in na amphiboles of the highly evolved units in contrast li in clinopyroxene are comparatively low b85 ppm and do not vary systematically with differentiation the distribution of li between amphibole and pyroxene is controlled by the major element composition of the minerals ca rich and na rich respectively and changes in oxygen fugacity due to li incorporation via coupled substitution with ferric iron during magmatic differentiation 7 li values of all minerals span a wide range from 17 to 8 with the different intrusive units of the complex having distinct li isotopic systematics amphiboles which dominate the li budget of whole rocks from the inner part of the complex have constant 7 li of 1 8 2 2 2 n 15 this value reflects a homogeneous melt reservoir and is consistent with their mantle derivation in agreement with published o and nd isotopic data clinopyroxenes of these samples are consistently lighter with 7 liamph cpx as large as 8 and are thus not in li isotope equilibrium these low values probably reflect late stage diffusion of li into clinopyroxene during final cooling of the rocks thus enriching the clinopyroxene in 6 li at the margin of the complex 7 li in the syenites increases systematically from 2 to high values of 14 this coupled with the observed li isotope systematics of the granitic country rocks reflects post magmatic open system processes occurring during final cooling of the intrusion although the shape and magnitude of the li isotope and elemental profiles through syenite and country rock are suggestive of diffusion driven isotope fractionation they cannot be modeled by one dimensional diffusive transport and point to circulation of a fluid having a high 7 li value possibly seawater along the chilled contact in all this study

organic geochemistry and basin modeling of late cretaceous harshiyat formation in the onshore and offshore basins in yemen implications for effective source rock potential and hydrocarbon generation abstract the purpose of this study is to present the source rock characteristics of late cretaceous harshiyat formation source rock in the onshore and offshore basins of yemen i e mukalla sayhut sayun masilah and jiza qamar source rock geochemical characterizations were completed and integrated to perform 1 d basin modeling to back predict source rock thermal maturation oil generation and expulsion the geochemical findings revealed that mudstone intervals within the harshiyat formation comprised favorable source rocks with total organic carbon toc content between 0 50 and 35 10 wt the organic matter intervals in the harshiyat mudstones are mainly types ii iii and iii kerogens with certain amount of type ii and i kerogens based on rock eval hi values ranging from 40 to 923 mg hc g toc mixed kerogen types were consistent with vitrinite and sapropelic organic matters as observed by visual kerogen examination and the distribution of biomarker fingerprints the existence of mixed types i ii and iii organic matter suggests that the harshiyat mudstones could contribute to oil and gas at sufficient thermal maturity levels the biomarker data of the organic matter in the harshiyat mudstones show that the source rock contains a mix marine phytoplanktonic bacteria terrestrial land plant enthronement and were deposited in suboxic anoxic conditions results of chemical and optical maturity indicators led to the conclusion of varying maturity stages from immature to late oil window levels for the mudstones of the harshiyat formation thermal maturation distributions inferred from the analyzed samples indicate that mudstone intervals in the offshore mukalla sayhut basin are extremely mature compatible with the late mature oil window and may have generated significant amounts of oil this interpretation was supported by strong geochemical similarity between the organic matter in the mudstones and those of the oils found in the offshore mukalla sayhut basin and demonstrated by the concentrations of n alkanes and isoprenoids as well as carbon isotopes in the offshore ras ghashwah 1x well burial and thermal models were constructed and used to address the effect of tectonic events in triggering oil generation and expulsion from mature harshiyat source rock in the offshore area kinetic database models for type ii and iii kerogen mixtures indicate that the initial conversion of kerogen to oil occurred since the late oligocene with transformation ratios tr that span between 10 and 50 furthermore the oil was expelled from organic matter intervals in the harshiyat source rock starting from late oligocene and continuing until late miocene with trs of 50 72 from that period up to the present the retained oil was cracked into wet gas in the gas window with an easy ro greater than 1 30 and with peak tr ratios greater than 72

magnetic studies of basement off the coast of bombay west of india abstract bathymetric and total magnetic intensity data along 45 closely spaced profiles in 20 100 m of water totalling 2400 line km were collected on the continental shelf off bombay west of india magnetic intensity anomaly maps were prepared the anomalies show prominent trends in e w nnw sse and ene wsw directions correlations of the anomaly signatures with the geology known from the drill well logs and seismic results infer 1 1 the mostly basaltic nature of the basement overlain by the tertiary sediments except in the murud depression and isolated patches of the bombay high and inner shelf where granites are interpreted 2 2 the lateral extent of the two nnw sse trending regional faults between longitudes 70 50 e and 71 40 e 3 3 the outlines of the magnetic signatures associated with the structural highs and depressions two dimensional model and spectral studies of the anomalies under numerical constraints have revealed the structure of the basement overlain by 1 5 5 0 km thick sediments a crustal section along a transect across the inner shelf the bassein high structure and the offshore basin in the middle shelf the bombay high structure in the middle outer shelf and further west is interpreted the section depicts the structure of the tertiary sediments the late cretaceous early tertiary basalts and the archaean precambrian granites thick basalt constructs occur in the paleoslopes of the archaean precambrian basement down faulting of parts of the western indian peninsula into the arabian sea along the regional faults is suggested due to the lithologically similar sequences of the tertiary sediments the basalts deccan traps and granitic gneisses of the study and onshore areas therefore the area is considered to be divided into three structural blocks consisting of the inner shelf the offshore basin and the bombay high separated by nnw sse trending deep seated faults which result from rifting of the crust the basement faults mostly extending to the overlying young sediments and the tectogenes indicate a continued stress regime the continued subsidence both mechanical and thermal of the crust in the study area under increased sediments the drift of the indian continent from the south to the present latitudes and the dynamic interaction of the oceanic continental lithospheres appear to deform the crust by thinning and shearing

influences of holocene sea level regional tectonics and fluvial gravity and slope currents induced sedimentation on the regional geomorphology of the continental slope off northwestern india abstract regional geomorphology derived from echosounding and bathymetric data lines of a total of 12 000 km depth to basement regional deep seated tectonic features surficial sediment distribution and holocene sedimentation rates of the continental margin off northwestern india are presented results indicate that the shelf edge over most of the region shelf break between 80 and 154 m water depth is covered with relict carbonate facies and partially buried bioherms of holocene age particularly off bombay and saurashtra regions significant changes in the depth and orientation of the shelf edge adjacent to saurashtra and the bombay high areas in relict carbonate facies are recorded at locations shelf edge depth is much more up to 150 m than the early holocene eustatic sea level still stand in this region about 100 m the upper boundary of the slope also varies considerably in depth about 1450 m in the vicinity of the indus fan having high sedimentation and 2900 m further southwards the gradient of the slope off the kachchh is steepest and some regional notches are observed at the upper slope the gentler slope off saurashtra and the bombay high area has large benches at depths of 180 230 m width 2 10 km and 650 780 m well below the holocene sea level the bombay high area has slope breaks between 400 and 600 m whereas off saurashtra steep breaks in the slope occur between 560 and 960 m depth further southwards at the foot of the slope elevations and depressions are present variations in the geomorphology of the slope off the northwestern continental margin of india are attributed to 1 late pleistocene holocene sea levels 2 regional tectonics 3 fluvial sedimentation and 4 gravity and slope currents induced sediment dynamics the locations under influences of slumping turbidity and tectonic movements with altered in situ sequence of sedimentations are delineated

source rock characteristics depositional setting and hydrocarbon generation potential of cretaceous coals and organic rich mudstones from gombe formation gongola sub basin northern benue trough ne nigeria abstract the ongoing exploration activities at the maiganga coal mine uncover some missing gaps in the stratigraphy of the late cretaceous gombe formation therefore there is a need to further investigate this sequence including the organic facies variations and distributions of the coals mudstones and sandy shaly sediments in the gombe sandstone formation gongola sub basin northern benue trough of northeastern nigeria geochemical and petrographic methods were used to assess the organic matter source input paleodepositional conditions thermal maturity and hydrocarbon generation potential of the analysed maiganga and yaya ngari samples field observations showed four coal seams interbedded with mudstones and shales deposited in coarsening upward sequence of a deltaic environment evaluation based on the source rock analyses sra reveals that maiganga sedimentary facies is dominated by terrestrial source input of type iii kerogen this is supported by the biomarker study suggesting land plant origin for the organic matter with minor lacustrine and marine influences in maiganga that grades into predominantly mixed organic matter input of a transitional terrestrial to marine environment in the yaya ngari area this shows a progressive movement towards marine source input paleodepositional conditions of organic matters were sub oxic to oxic in maiganga while the mixed organic matters in yaya ngari were deposited in sub oxic conditions based on organic petrology and bitumen extraction data the maiganga coal was distinctly observed to be immature of pre oil generation window while the yaya ngari is in early oil generation window these analysed sediments are mainly gas prone based on the dominance of type iii kerogen although the presence of type ii iii kerogen supported by relatively higher hi may indicate gas oil potential for the maiganga coal on the other hand type iv kerogen dominated the yaya ngari samples this suggests that these shales are gas prone or do not possess any hydrocarbon generation potential as indicated by the very low hi values

rare earth elements in apatite uptake from h2o bearing phosphate fluoride melts and the role of volatile components the partitioning of rare earth elements rees between fluorapatite fap and h sub 2 o bearing phosphate fluoride melts has been studied at about 700 and 800 degrees c and 0 10 0 15 gpa ree uptake patterns i e plots of d ree fap melt are convex upwards and peak near nd for single ree substituted fap at minor 0 03 0 25 wt ree sub 2 o sub 3 abundances and binary lree hree substituted fap and hexa ree substituted fap at minor to major 0 25 7 8 wt ree sub 2 o sub 3 abundances partition coefficients for minor abundances of ree and depolymerized phosphate melts are about 5 8 and 1 for la nd and lu respectively and broadly comparable to those for early fluorapatite in the fractionation of melts of basaltic composition the ca2 site exerts marked control on the selectivity of apatite for ree because it preferentially incorporates lree and its effective size varies with substitution of the a site volatile anion component f cl oh using simple crystal chemical arguments melt or fluid normalized ree patterns are predicted to peak near nd for fluorapatite and be more lree enriched for chlorapatite these predictions are consistent with data from natural rocks and laboratory experiments the wide variation in d ree apatite melt in nature from 1 for whitlockite bearing lunar rocks to about 100 for evolved alkalic rocks ismore attributed largely to the influence of the volatile components 49 refs 8 figs 3 tabs less

origin of crude oils from oilfields in the zagros fold belt southern iraq relation to organic matter input and paleoenvironmental conditions crude oil samples from cretaceous and tertiary reservoir sections in the zagros fold belt oil fields southern iraq were investigated using non biomarker and biomarker parameters the results of this study have been used to assess source of organic matter and the genetic link between oils and their potential source rocks in the basin the oils are characterized by high sulphur and trace metal ni v contents and relatively low api gravity values 17 4 22 7 api this indicates that these oils are heavy and generated from a marine source rock containing type ii s kerogen this is supported by their biomarker distributions of normal alkanes regular isoprenoids terpanes and steranes and the bulk carbon isotope compositions of their saturated and aromatic hydrocarbons the oils are characterized by low pr ph ratios 1 high values of the c35 homohopane index and c31 22r c30 hopane ratios relatively high c27 sterane concentrations and the predominance of c29 norhopane these biomarkers suggest that the oils were generated predominantly from a marine carbonate source rock deposited under reducing conditions and containing plankton algal and microorganisms source input the presence of gammacerane also suggests water column stratification during source rock deposition the biomarker characteristics of the oils are consistent with those of the middle jurassic sargelu carbonate as the effective source rock in the basin biomarker maturity data indicate that the oils were generated from early maturity source rocks

organic geochemical characteristics of crude oils and oil source rock correlation in the sunah oilfield masila region eastern yemen abstract the objective of this study is to provide information on source organic matter input depositional conditions and the correlation between crude oils recovered from sunah oilfield and upper jurassic madbi formation a suite of twenty six crude oils from the lower cretaceous reservoirs qishn clastic of the masila region eastern yemen were analysed and geochemically compared with extracts from source rock of the upper jurassic madbi formation the investigated biomarkers indicated that the sunah oils were derived from mixed marine and terrigenous organic matter and deposited under suboxic conditions this has been achieved from normal alkane and acyclic isoprenoids distributions terpane and sterane biomarkers these oils were also generated from source rock with a wide range of thermal maturity and ranging from early mature to peak oil window based on molecular indicators of organic source input and depositional environment diagnostic biomarkers one petroleum system operates in the masila region this derived from upper jurassic madbi organic rich shales as source rock therefore the hydrocarbon exploration processes should be focused on the known location of the upper jurassic madbi strata for predicting the source kitchen

apatite liquid partition coefficients for the rare earth elements and strontium abstract sixteen sets of apatite liquid partition coefficients dap liq for the rare earth elements ree la sm dy lu and six values for sr were experimentally determined in natural systems ranging from basanite to granite the apatite melt glass assemblages were obtained from starting glasses artificially enriched in ree sr and fluorapatite components these were run under dry and hydrous conditions of 7 5 20 kbar and 950 1120 c in a solid media piston cylinder apparatus an sem equipped electron microprobe was used for subsequent measurement of ree and sr concentrations in coexisting apatites and quenched glasses the resulting partition coefficient patterns resemble previously determined apatite phenocryst groundmass concentration ratios in the following respects 1 the rare earth patterns are uniformly concave downward i e the middle ree are more compatible in apatite than the light and heavy ree 2 dreeap liq is much higher for silicic melts than for basic ones and 3 strontium and therefore eu2 is less concentrated by apatite than are the trivalent ree the effects of both temperature and melt composition on dreeap liq are systematic and pronounced at 950 c for example a change in melt sio2 content from 50 to 68 wt causes the average ree partition coefficient to increase from 7 to 30 a 130 c increase in temperature on the other hand results in a two fold decrease in dreeap liq partitioning of sr is insenstitive to changes in melt composition and temperature and neither the sr nor the ree partition coefficients appear to be affected by variations in pressure or h2o content of the melt the experimentally determined partition coefficients can be used not only in trace element modelling but also to distinguish apatite phenocrysts from xenocrysts in rocks reported apatite megacryst host basalt ree concentration ratios 12 for example are considerably higher than the equilibrium partition coefficients which suggest that in this particular case the apatite is actually xenocrystic a reversal experiment incorporated in our study yielded diffusion profiles of ree in apatite from which we extracted a ree ca interdiffusion coefficient of 2 4 10 14 cm2 s at 1120 c extrapolated downward to crustal temperatures this low value suggests that complete ree equilibrium between felsic partial melts and residual apatite is rarely established

geochemical characteristics of crude oils their asphaltene and related organic matter source inputs from fula oilfields in the muglad basin sudan abstract bulk geochemical characteristics of crude oils coupled with geochemical analyses of reservoir oil asphaltenes from fula oilfields in the muglad basin have provided information on source organic matter input depositional environment and the correlation between these crude oils and their potential source rocks in the basin only one oil family is present within the fula oilfields as indicated by biomarker and non biomarker parameters the fula oils are characterized by moderate api gravity low sulphur and moderate trace metal ni v contents and high wax contents this suggested that the oils were generated from source rock that was deposited in a principally lacustrine environment this is supported by bulk geochemical characteristics and biomarker compositions a variety of biomarker specific parameters obtained from n alkanes regular isoprenoids terpanes and steranes indicate that the fula oils were generated predominantly from algae derived organic matter that was deposited in a lacustrine environment which then experienced a slight seawater influence under suboxic to relatively anoxic conditions these oils were generated from source rock with a wide range of thermal maturity ranging from early to peak oil window the biomarker characteristics of these oils are consistent with those of the early cretaceous abu gabra shales the oil source rock relationship is also demonstrated by similarities in the structural moieties of the fula oil asphaltene and the abu gabra shale kerogens the pyrolysis gc of the analyzed fula oil asphaltene indicates that the oils were derived from type i algal organic matter consistent with paraffinic high wax oils

secular and environmental constraints on the occurrence of dinosterane in sediments abstract the distribution patterns of sedimentary a ring methylated steranes have changed markedly over geological time although dinosterane and its isomer 24 ethyl 4 methylcholestane have been tentatively identified in three proterozoic rock units they are either not detectable or occur in low abundance relative to 3 methyl steranes throughout most of the palaeozoic between permian and middle triassic times 260 220 ma ago 4 methyl sterane abundances in marine sediments increased markedly the presence of dinosterane in some middle triassic marine sediments is contemporaneous with the appearance of fossil cysts of uncontested dinoflagellate affinity 4 methyl steranes including dinosterane or their precursor sterenes and sterols then show a continuous presence often in high abundance in marine sediments from the late triassic through to the present day assemblages of 4 methyl steranes and their precursors but with dinosterane absent or in low relative abundance are often the predominant steroids in lacustrine sediments in the cainozoic dinosterane appears to arise predominantly from marine dinoflagellates and as a consequence is a useful biological marker for mesozoic and cainozoic marine organic matter the isomer 24 ethyl 4 methylcholestane is likely to have multiple origins although its very high abundance in tertiary lacustrine sediments and oils compared to older materials suggests that dinoflagellates could also be the source in these cases

crustal structure from deep seismic soundings along the koyna ii kelsi loni profile in the deccan trap area india abstract the crustal depth section obtained from deep seismic soundings along the koyna ii kelsi loni profile which lies near latitude 18 n roughly in the east west direction in that part of the deccan trap maharashtra state india shows a number of reflection segments below the deccan traps down to the moho discontinuity a deep fault below the deccan traps 13 km east of mahad divides the entire cross section including the moho boundary into two crustal blocks the reflection segments show updip towards the west coast in the western block the moho discontinuity which is at a depth of 39 km near the deep fault starts rising towards the coast reaching a depth of 31 5 km at the west coast the eastern block is thrown up by 1 5 km with respect to the western block along the deep fault a structural contour map of the moho discontinuity for the koyna reservoir area has been prepared from the present results and the crustal information obtained along the koyna i profile kaila et al 1979a shows that the deep fault in the koyna area is aligned in the nnw sse direction refraction seismic data analysis by the wave front method reveals that the thickness of the deccan trap increases towards the west coast the deccan trap is 600 700 m thick in the eastern region between nira sp 130 and loni sp 200 and attains a thickness of 1500 m at 10 km east of the west coast the longitudinal wave velocity in the deccan traps along the profile varies from 4 8 to 5 0 km sec and in the crystalline basement from 6 0 to 6 15 km sec a tentative isopach contour map of the deccan traps and a tentative structural contour map of the pre deccan trap contact have been prepared for the koyna reservoir area from the results along the koyna ii and koyna i profiles a flexure aligned in a nnw sse direction in the pre deccan trap contact which is an expression of the deep fault into the basement has been clearly brought out the flexure coincides in general with the orientation of the deccan volcanic scarp in this area

geochemical characteristics of terrigenous and marine sourced oils in hokkaido japan abstract crude oils in hokkaido japan are divided into two genetic groups based on bulk properties carbon isotope compositions and biomarker distributions one group is characterized by high carbon isotope canonical variables sofer 1984 high wax and low sulfur content high pr ph ratios low c27 c27 c29 sterane ratios relatively low ts ts tm ratios and the absence of tricyclic terpanes and c35 homohopanes these characteristics suggest that the oils were generated mainly from terrigenous organic matter in source rocks deposited under highly oxic conditions the other group is characterized by low canonical variables low wax and high sulfur content low pr ph ratios high c27 c27 c29 sterane ratios relatively high ts ts tm ratios and the presence of tricyclic terpanes and c35 homohopanes properties that suggest that they were generated from marine shales based on the biomarker distributions the terrigenous oils correlate to paleogene coals and coaly shales whereas the marine oils correlate to miocene marine shales the atomic h c ratios of the coals indicate that they have oil generating potential the geographic distribution of the terrigenous and marine source rocks and their thermal maturity control the distribution of the oils in hokkaido the geographic distribution of the paleogene coal bearing formations corresponds to the distribution of the terrigenous oils in central hokkaido the marine oils are restricted either to areas of high heat flow related to volcanic activity or to the area with thick neogene and quaternary sediments where the miocene source rocks are buried deep enough for oil generation

gravity anomalies and crustal structure of the western continental margin off goa and mulki india abstract bathymetric and gravity data totalling 2000 line kilometres on the continental margin off goa and mulki india have been studied and prominent nnw sse and ene wsw trending free air gravity anomalies varying between 60 and 25 mgal have been identified using constraints from seismic refraction and reflection and well log results the thicknesses of the layers are estimated by computing two dimensional crustal structure models for the free air gravity anomalies the study suggests that 1 there are three layers varying in thickness from 0 5 to 4 0 km 0 5 to 12 0 km and from 14 0 to 26 0 km with densities of 2 3 2 6 and 2 9 g cm 3 which are interpreted as sedimentary granitic and mafic basaltic layers respectively that 2 there is a maximum thickness of 4 0 km of sediment over the shelf margin basin and that 3 the moho occurs at a depth of 24 30 km

the qishn formation yemen lithofacies and hydrocarbon habitat abstract the barremian aptian qishn formation of yemen is broadly described in the context of its role as the lowest widespread transgressive unit of the cretaceous system in the country and of the two laterally equivalent lithofacies groups that reflect the advance of the cretaceous sea from east to west this is undertaken against the background of the tectonic events that preceded its deposition and those that followed it during the remainder of the cretaceous so as to better understand its hydrocarbon habitat the qishn formation clastics sands have proved to be an excellent and major oil reservoir in eight recent oil discoveries made in the area between the mukalla and hoowarin highs of the hadhramaut province of yemen the oil in these discoveries like the oil and gas in 14 of the currently remaining 15 fields and discoveries in the country is generated from upper jurassic organic rich source rocks and vertically charged the qishn reservoir in the absence of an effective intervening seal subsurface data from the recent discoveries area and from sparse subsurface control in the jeza basin to its east indicate the presence in this region of an areally more limited pre qishn cretaceous platform sequence and suggests that the jeza basin was an early cretaceous marine embayment between still positive land masses on either side in which thicker cretaceous sequences continued to be laid down after the bordering areas were inundated by the qishn transgression these basinal sequences probably include qishn source shale levels similar to those found in the southern offshore area there they are mainly immature however or else do not appear to have generated identifiable trapped oil the jeza basin thus appears to hold promising untested potential for oil sourced by unpenetrated qishn levels in addition to good upper cretaceous mukalla formation source levels and upper jurassic levels where preserved and not too deeply buried which would be at varying degrees of oil and gas maturity these sources could charge by multi stage migration from the kitchen areas various cretaceous reservoirs including qishn clastics or carbonates in any updip traps

pristane phytane ratios in the mineralized kupferschiefer of the fore sudetic monocline southwest poland abstract the interaction of organic matter with fluids is important in geochemical processes in surface and diagenetic environments in the kupferschiefer copper deposits of southwestern poland organic fluid interactions are inferred to have been important in the genesis of the ore deposits previous organic geochemical studies of the kupferschiefer report evidence of a late diagenetic oxidation event that altered the organic geochemistry this study uses the saturated hydrocarbons as indicators of the biological input and the earliest diagenetic processes to affect the organic geochemistry of the kupferschiefer the normal alkane distributions are lithofacies controlled indicating that they reflect biological input the ratio of the saturated isoprenoids pristane phytane are potential indicators of the redox conditions during sedimentation and diagenesis very low pr ph ratios are associated with lithofacies that were deposited in hypersaline environments increases in the pr ph ratio within individual traverses are interpreted as indicating increasing oxidation of organic matter during deposition and early diagenesis trends of increasing pristane phytane ratios are observed at the base of the kupferschiefer and at the transition within the kupferschiefer from the clay rich to the carbonate rich kupferschiefer which corresponds approximately to the transition from cu zone to the pb zone early diagenetic copper depleted cu and cu fe sulfides have also been reported form the top of the weissliegendes and the cu zone pb zone transition and it is conceivable that both could be related to the same processes

correlation of different maturity parameters in the ahmedabad mehsana block of the cambay basin abstract the potential use of organic matter maturation parameters in assessing the diagenetic catagenetic transition zone with the help of various known molecular parameters has been investigated in the ahmedabad mehsana block of the cambay basin a set of 24 conventional cores from the eocene shales covering a depth regime of 922 2500 m has been studied the oil generation threshold i e the boundary between the diagenetic and catagenetic maturation regimes is assessed to be at 1800 m based on a combination of parameters including percent hydrocarbons in eom saturate aromatic hydrocarbon ratio in eom and the rock eval production index the pr n c17 ratio rock eval hi and oi were not suitable for reliable maturation profiling nor for independently indexing the stages of maturation the extent of the catagenetic regime is distinguished by ph n c18 ratios

molecular organic geochemistry of the tarim basin northwest china we conducted organic geochemical analyses on the largest suite of oils and source rock extracts from the tarim basin northwest china currently available statistical cluster analysis of the entire suite of tarim oils distinguishes at least seven genetic groups of oils the largest group of oils was collected from the tazhong and tabei uplifts and originated from marine middle upper ordovician anoxic marls that mark slope facies at the margins of structural uplifts two other genetic groups most likely originated from marine middle upper ordovician source rocks but of distinct facies with one an oxic shale rich source west of the bachu uplift and the other an anoxic shale source at tazhong

whole rock phosphate and silicate compositional trends across an amphibolite to granulite facies transition tamil nadu india chemical trends from north amphibolite facies to south granulite facies along a 95 km traverse in tamil nadu southern india include whole rock depletion of rb cs th and u enrichment in ti and f and depletion in fe and mn in biotite and amphibole increases in al and decreases in mn in orthopyroxene enrichment of fluorapatite in f k feldspar blebs are widespread along quartz plagioclase grain boundaries and could indicate either partial melting or metasomatism in the northernmost portion of the traverse the principal rare earth element ree bearing minerals are allanite and titanite south of a clinopyroxene isograd monazite grains independent of fluorapatite are the major ree and th bearing phase further south independent monazite is rare but th free monazite inclusions are common in fluorapatite during prograde metamorphism independent monazite was replaced by ree rich fluorapatite in which the monazite inclusions later formed the loss of independent monazite was accompanied by a loss of whole rock th and possibly a small depletion in light ree most mineralogical features along the traverse can be accounted for by progressive dehydration and oxidation reactions trace element depletion is best explained by the action of an externally derived low h2o activity brine migrating from a source at greater depth possibly preceded or accompanied by partial melting

marine magnetic anomalies off ratnagiri western continental shelf of india abstract total magnetic intensity and bathymetric surveys were carried out in the offshore area of ratnagiri on the western continental shelf of india and an isomagnetic anomalies map at a contour interval of 50 nt was prepared which reveals n s trends of magnetic anomalies two dimensional model and spectral studies of these anomalies were carried out and subsurface models of the geology in the area have been derived from anomalies at a number of places the results suggest that the anomalies occur over a magnetic crystalline basement at a depth of 1 1 2 km which is similar in magnetization to onshore basalts of northwest india these anomalies are believed to be an expression of a considerable thickness around 1 7 km of basalt underlain by sediments identification of these basalts in offshore areas along the northwestern continental shelf of india would support 1 the idea that the onshore deccan basalts of western india and the rhyolitic tuffs at the laccadive ridge system dsdp site 210 are related to the same volcanic events and 2 subsequent downfaulting of onshore deccan basalts into the arabian sea and submergence below the tertiary sediments

the panvel flexure along the western indian continental margin an extensional fault structure related to deccan magmatism abstract on the basis of field observations aided by remote sensing data a new model for the western indian panvel flexure is proposed the model involves normal motion on east dipping faults and westward tilting of fault blocks the flexuring occurred by attenuation and foundering of continental crust due to crustal thinning and loading by a dyke swarm following a period of massive magmatic discharge accompanying the continental break up and opening of indian ocean during early tertiary times

geochemical and petrographic characterization of organic matter in the upper jurassic madbi shale succession masila basin yemen origin type and preservation the upper jurassic madbi formation located in the masila basin eastern yemen represents the major source rock in this basin organic rich shales from two oilfields kharir and wadi taribah were analysed to evaluate the type and origin of the organic matter and to determine the factors controlling its deposition this study is based on geochemical analyses of whole rock total organic carbon content rock eval pyrolysis and carbon isotope data and petrographic analyses on organic matter kerogen maceral composition and palynofacies by optical and scanning electron microscopy organic petrographic composition of kerogen shows that the madbi shale is characterized by high amounts of organic matter consisting predominantly of yellow fluorescing amorphous organic matter and alginite of marine origin terrigenous organic materials such as vitrinite spores and pollen are present in low quantities the predominance of marine plankton as indicated by visual kerogen analysis is consistent with reported carbon isotopic values it appears that the high amounts of organic matter in the madbi shale succession might be mainly due to good preservation under suboxic anoxic conditions consequently the madbi shales possess very good petroleum generative potential owing to high content of hydrogen rich type ii and i oil prone kerogen

flexural and stratigraphic development of the west indian continental margin subsidence curves for 27 wells from the western continental margin of india show a characteristic late oligocene to early miocene 24 5 ma rapid increase in subsidence rate superposed on the long lived slow subsidence typical of the thermal subsidence phase of passive continental margins by subtracting a best fit negative exponential subsidence from the observed subsidence curves we obtain an estimate of the distribution and magnitude of the excess subsidence affecting the neogene development of the west indian margin the magnitude of this excess subsidence increases seaward from the coast ranging from a few meters to 2000 m near the shelf edge we examine the following hypotheses to explain the distribution and timing of this excess subsidence 1 modification of basin stratigraphy due to the effects of lithospheric in plane compression 2 creation of accommodation space on the margin by flexural effects associated with indus fan loading and 3 rapid growth of the continental margin and associated flexural effects of the three hypotheses tested the least important mechanism to account for the observed excess subsidence is that of variations of lithospheric in plane force principally because maximum in plane compression within the indo australian plate was only achieved in the late miocene because indus fan sediment deposition began in the late oligocene to early miocene we investigated three dimensional flexural effects associated with fan loading as a cause of the excess subsidence beginning at 24 ma the distribution and magnitude of modeled flexural deflection however are not consistent with the observed excess subsidence interpretation of seismic reflection data indicates that the margin has aggraded and prograded by 100 km basin ward since the oligocene therefore we evaluate the flexural effects of this margin growth by estimating the amount of space infilled by margin progradation and aggradation since 24 ma and computing the resulting deflection this deflection matches the distribution and magnitude of observed excess subsidence along the margin in addition the distribution of the flexural bulge predicted from the combined deflections due to indus fan and margin loading is spatially coincident with the distribution of exposed marine terraces and drainage divides in the saurastra peninsula and the regions surrounding the gulfs of cambay and kutch respectively available gravity seismic reflection refraction and well data are consistent with our prediction of a 4000 to 5000 m thick sediment load developed during the neogene along the outer margin we propose that flexural deformation due to sedimentary loading provides a potential tectonic feedback mechanism that affects coastal and fluvial depositional processes as regions in close proximity to the load are depressed regions farther from the load experience uplift i e the peripheral bulge which is sufficient to cause subaerial exposure of large portions of the shelf and to modify existing drainage networks this feedback represents a mechanism for inducing relative sea level changes without invoking glacial eustasy

stable carbon isotope compositions of crude oils application to source depositional environments and petroleum alteration the carbon isotopic composition of the c15 saturate and aromatic hydrocarbon fractions and the gas chromatographs of the c15 saturate fraction of 339 oils were geochemically and statistically evaluated results of this study show that the average isotopic compositions of the c15 aromatic hydrocarbon fractions of oils sourced from terrigenous or marine organic matter are identical the average isotopic composition of the c15 saturate fraction of oils derived from terrigenous organic sources is slightly more negative 0 9 pmil than the average for marine oils but this difference is insufficient to be used as a reliable source indicator reports in the literature stating that marine oils are isotopically more positive than te rigenous oils and that the difference can be utilized to distinguish between the two are therefore not supported by this study the isotopic differences between oils sourced from terrigenous and marine organic matter do not manifest themselves in the range of absolute values of one oil fraction but rather in the isotopic relationship between the saturate and aromatic hydrocarbon fractions the isotopic relationship is the following oils of terrigenous organic source dgr13caro 1 12 dgr13csat 5 45 oils of marine organic source dgr13caro 1 10 dgr13csat 3 75 the difference between the two equations was evaluated statistically and a statistical parameter cv the canonical variable cv 2 53 dgr13csat 2 22 dgr13caro 11 65 was used to distinguish between marine and terrigenous oils cv values larger than 0 47 indicate predominantly a terrigenous organic source for the oil whereas cv values smaller than 0 47 indicate mostly a marine organic source thermal maturity differences in oils and isotopic variations in the source beds can cause as much as 2 pmil variations in the isotopic composition of one family of oils finally stable carbon isotopes can in some situations help correlate biodegraded oils to their nondegraded counterparts

early eocene equatorial vegetation and depositional environment biomarker and palynological evidences from a lignite bearing sequence of cambay basin western india abstract an investigation of palaeofloral distribution with depositional environment and palaeoclimatic condition of western indian subcontinent during early eocene period has been carried out from a lignite bearing succession of cambay basin western india the study of biomarkers palynological remains and petrography is taken as proxies for providing supportive evidence for our inference the petrographic results reveal that the sediments are thermally immature and coalification was extended up to the lignitic stage low rank b the palynological results show the dominance of angiosperms mainly members belonging to the arecaceae family throughout the studied section triterpenoids with oleanane ursane and lupane structure in extractable organic matter are derived from angiosperm wax pollen grains spinizonocolpites proxapertites dipterocarpuspollenites albertipollenites retipollenites arengapollenites lakiapollis and longapertites with pteridophyte spores and fungal fruiting bodies confirm the prevalence of tropical to subtropical climate during the deposition of the sediments sesquiterpenoids like longifolene 12 methanoazulene cadinane and selinene together with amyrin derivatives are the indicator of dipterocarpaceae family that grows in the extant tropical rain forests in se asia appearance of dinoflagellate cysts and the predominance of lower molecular weight part in n alkane series with the signature of submerged floating vegetation in the shale horizon indicate marine influence in the younger part of the mine section the presence of mangrove pollen such as spinizonocolpites proxapertites and acanthotricolpites further suggests that the lignite bearing sequence was deposited in marshy marginal marine environment

apatite in the ilimaussaq alkaline complex occurrence zonation and compositional variation abstract apatite from the augite syenite and the roof sequence of layered nepheline syenites pulaskite foyaite sodalite foyaite and naujaite of the ilimaussaq alkaline complex has been analysed by electron microprobe for ca p na si selected rare earth elements ree f and cl in the augite syenite chilled facies and middle zone euhedral apatite crystals are relatively abundant as inclusions in other liquidus phases the ree content is ca 1 wt ree 2 o 3 the same level is found in interstitial apatite in the coarse grained innermost facies ree enriched intercumulus apatite overgrowths are common and can have up to ca 18 wt ree 2 o 3 apatite is a common phase in the pulaskite and foyaite whereas it is rare in the sodalite foyaite and naujaite based on compositional variation and zoning it is possible to distinguish four generations of apatite in the layered roof sequence 1 primary apatite belonging to the high temperature mineral assemblage this apatite occurs in the pulaskite foyaite and sodalite foyaite as oscillatory zoned crystals whereas only remnants are found in the naujaite the ree enrichment is dominated by the ca 2 p 5 ree 3 si 4 substitution and maximum ree 2 o 3 exceeds 20 wt 2 irregularly zoned apatite occurs as rim zones on the primary apatite in the foyaite and as the dominant type of apatite in the sodalite foyaite and naujaite most irregularly zoned grains are altered primary apatite during the dissolution and recrystallisation process the composition gradually changed towards a lower ree content 3 overgrowths of homogeneous apatite on the irregularly zoned apatite in the naujaite 4 na and ree rich apatites occur in the foyaite sodalite foyaite and naujaite either as overgrowths on earlier generations of apatite or as individual crystals calculated chondrite normalised patterns show that the later generations of apatite are relatively enriched in lree and depleted in hree the most pronounced evolution is found in na and ree rich apatite apatite melt partition coefficients for la ce nd sm dy y and yb are calculated for the augite syenite and nepheline syenites of the roof sequence the coefficients show the characteristic convex shape with a maximum around nd and sm using the calculated partition coefficients and the chemical composition of the na and ree rich apatite the ree content of a late aqpaitic melt in the roof sequence is estimated the shape of the chondrite normalised pattern is similar to that of a late arfvedsonite lujavrite dyke and steeper than the patterns of the primary magma

organic geochemistry palynofacies and petroleum potential of the mukalla formation late cretaceous block 16 eastern yemen abstract the late cretaceous mukalla formation of the mahra group is present in the subsurface of eastern yemen the palynofacies thermal maturation and hydrocarbon potential of this formation recorded from three exploratory wells in the qamar basin are discussed two of the wells are in the offshore part of block 16 and one is in the onshore part both organic geochemical and palynofacies analyses indicate that the formation contains oil and gas prone kerogen rock eval pyrolysis and gas chromatography data show a peak thermal maturation stage for organic matter types ii iii and iii and good conditions for hydrocarbon generation and expulsion three major palynofacies types are identified through the succession these indicate open marine marginal to shallow marine and fluvio deltaic environments reflecting multiple marine transgressive and regressive phases during the period of deposition of the formation which took place in a humid subtropical to tropical climate

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

organic geochemistry characterization of the paleogene to neogene source rocks in the sayhut subbasin gulf of aden basin with emphasis on organic matter input and petroleum generation potential paleogene umm er radhuma and ghaydah and neogene sarar source rocks from sayhut subbasin in the gulf of aden basin were studied to provide information such as organic matter types paleoenvironmental conditions and petroleum generation potential this study is based on whole rock organic geochemical analyses and organic petrology the total organic carbon toc contents of the paleogene to neogene source rocks range from 0 43 to 6 11 with an average toc value of 1 00 indicating fair to very good source rock potential the paleogene ghaydah and umm er radhuma source rocks are relatively higher in genetic petroleum potential than neogene sarar source rocks mainly oil and gas are anticipated from the ghaydah and umm er radhuma source rocks with hydrogen index hi values ranging from 95 to 715 mg hydrocarbon hc g toc this is supported by the presence of significant amounts of liptinite macerals in the ghaydah and umm er radhuma source rocks the sarar source rocks are dominated by vitrinitic type iii kerogen hi 200 mg hc g toc and are thus considered to be gas source rocks the paleogene to neogene source rocks have vitrinite reflectance r o values in the range between 0 30 and 0 77 r o and pyrolysis maximum temperature values range from 412 c to 444 c 774 f to 831 f consistent with the immature to early mature oil window therefore the present day kerogen type in the paleogene to neogene source rocks is original and should not have been altered by thermal maturity the biomarker of organic matter suggests that the paleogene to neogene source rocks were deposited in a marine environment under suboxic to anoxic conditions the biomarkers also indicate that the paleogene to neogene source rocks contain a mixture of aquatic organic matter planktonic and bacterial and terrigenous organic matter with increasing terrigenous influence to sarar source rock samples highly hypersaline reducing conditions are also evidenced in ghaydah and umm er radhuma source rocks as indicated by the presence of the gammacerane biomarker low pristane to phytane ratios and homohopane distribution patterns

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

apatite in igneous systems apatite is a minor but ubiquitous mineral in most igneous rocks although the modal proportion of apatite in common rocks is generally low it can reach high concentrations in enclaves cumulates and other rocks of low abundance i e rocks that constitute a small volume of the crust and mantle e g nelsonites the presence of apatite in most rocks is due not only to its low solubility in naturally occurring melts and aqueous solutions but also to the limited ability of common rock forming minerals to accept the amount of phosphorus that occurs in most rocks into their structure in this paper we will discuss some aspects of the occurrence texture composition physical chemistry and petrogenetic significance of apatite in felsic rocks i e andesite to rhyolite and their plutonic analogs in mafic i e basalts and related rocks and plutonic analogs and ultramafic rocks of the earth s crust and mantle fluorapatite is by far the most common member of apatite family found in igneous rocks however most natural fluorapatite contains some chlorine and hydroxyl as well and these constituents can attain high concentrations in some cases the other halogens bromine and iodine also occur in apatite but their concentrations are much lower than chlorine and fluorine many cations commonly substitute for calcium and phosphorus in apatite however they rarely reach concentrations that warrant the definition of a separate mineral species apatite can be described by the general formula a5 xo4 3z following sommerauer and katz lehnert 1985 the a site accommodates large cations e g ca2 sr2 pb2 ba2 mg2 mn2 fe2 ree3 eu2 cd2 na pan and fleet ch 2 in this volume and comprises two sites that exhibit vii fold

organic geochemical characteristics of crude oils from the masila basin eastern yemen the masila basin is an important hydrocarbon province in yemen but the origin of hydrocarbons and their generation history are not fully understood in this regard 10 crude oils from different petroleum reservoir sections in the masila basin were characterized by a variety of biomarker and non biomarker parameters using gc gc ms and stable carbon isotope techniques oils from the masila basin display pristane phytane pr ph ratios ranging from 1 7 to 2 0 low sulfur content high c35 homohopane index relatively high c27 sterane concentrations and relatively high tricyclic terpanes suggesting a marine clay source rock that was deposited in mildly anoxic to suboxic conditions with dominantly algal organic matter c29 20s 20s 20r steranes and bb bb aa sterane ratios indicate that the masila oils have reached peak oil window maturity another related feature of these oils is the absence of 18a h oleanane which suggests a source age older than cretaceous the carbon isotope compositions are similar to those of the potential source rocks which range from 25 4 to 28 3 indicating a marine environment the new data presented in this paper suggest that the masila oils constitute one oil family and that the oil originated from the upper jurassic madbi source rock in the basin