environmental change during the early cretaceous in the purbeck type durlston bay section dorset southern england a biomarker approach abstract the purbeck type section durlston bay dorset uk exhibits littoral lagoonal to lacustrine facies it shows a gradual climatic environmental change from semi arid conditions associated with evaporites at the jurassic cretaceous transition to a more humid climate at the end of the berriasian though generally organic poor total organic carbon toc the distribution of alkanes hopanes and steranes indicates that the origin of the om is mainly algal bacterial and only changed moderately with the climatic evolution the saline and anoxic bottom water conditions indicated for most of the samples point to the recurrence of salinity stratification within the basin a high contribution of odd numbered c 23 c 31 n alkanes from algaenan containing freshwater algae in particular botryococcus is noted for all the samples despite the low abundance of these organisms in the corresponding palynofacies this prominence probably results from the high resistance to degradation and the selective preservation of botryococcus related lipids the subtle balance of aridity and freshwater inputs favoured both an abundance of botryococcus and the development of anoxia leading to the enhanced preservation of om during the intermediate climatic episode while the conditions were less favourable during the semi arid and more humid episodes

a tale of shales the relative roles of production decomposition and dilution in the accumulation of organic rich strata middle upper devonian appalachian basin abstract a new consensus on the processes responsible for organic carbon burial in ancient epeiric seas has emerged more firmly grounded in the uniformitarian framework of modern oceanography and biogeochemistry this consensus recognizes the interdependent roles of sedimentation primary production and microbial metabolism in favor of earlier end member models e g production vs preservation in this study one of the classic stratigraphic sequences upon which the preservation end member was based is re interpreted in light of this new consensus the study employs an extensive new sedimentological biogeochemical database from cores drilled in western new york the database spans over 500 m and 15 my of devonian deposition in the appalachian basin and provides a framework for comparative study of organic matter burial the major conclusions are 1 few organic rich units were deposited under pervasive anoxic sulfidic water columns 2 establishment and breakdown of seasonal thermoclines on annual or longer timescales were the predominant mode of stratification and 3 under such conditions remineralization of bio limiting nutrients may have played a key role in organic matter burial by creating a eutrophication pump this pump may have augmented an already rising nutrient inventory such that productivity levels exceeded the threshold required for development of suboxic to anoxic conditions in sediments and episodically in bottom waters a final conclusion asserts that the master variable for organic matter accumulation was relative sea level change which exerted influence on clastic dilution preservation and production processes sea level rise events led to sediment starvation and organic carbon concentration in distal basin sediments as well as to decreased effectiveness of seasonal mixing and thus longer build up intervals for remineralized nutrients episodic mixing of nutrient enriched bottom waters led to enhanced production ultimately increased clastic sediment delivery and water column mixing during relative sea level fall diluted surface sediment organic content such that respiratory demand could be met by increased oxygen supply thus terminating deposition of strata enriched in organic carbon

earthquakes gravity and the origin of the bali basin an example of a nascent continental fold and thrust belt we infer from the bathymetry and gravity field and from the source mechanisms and depths of the eight largest earthquakes in the bali region that the bali basin is a downwarp in the crust of the sunda shelf produced and maintained by thrusting along the flores back arc thrust zone earthquake source mechanisms and focal depths are inferred from the inversion of long period p and sh waves for all events and short period p waves for two of the events centroidal depths that give the best fit to the seismograms range from 10 to 18 km but uncertainties in depth allow a range from 7 to 24 km the p wave nodal planes that dip south at 13 to 35 7 strike roughly parallel to the volcanic arc and are consistent with thrusting of crust of the bali basin beneath it the positions of the earthquakes with respect to crustal features inferred from seismic and gravity data suggest that the earthquakes occur in the basement along the western end of the flores thrust zone the slip direction for the back arc thrust zone inferred from the orientation of the earthquake slip vectors indicates that the thrusting in the bali basin is probably part of the overall plate convergence as it roughly coincides with the convergence direction between the sunda arc and the indian ocean plate summation of seismic moments of earthquakes between 1960 and 1985 suggests a minimum rate of convergence across the thrust zone of 4 2 mm a the presence of back arc thrusting suggests that some coupling between the indian ocean plate and the sunda arc occurs but mechanisms such as continental collision or a shallow subduction of the indian ocean plate probably can be ruled out the present tectonic setting and structure of the bali basin is comparable to the early forelands of the andes or western north america in that a fold and thrust belt is forming on the continental side of an arc trench system at which oceanic lithosphere is being subducted the bali basin is flanked by the tertiary java basin to the west and the oceanic flores basin to the east and thus provides an actualistic setting for the development of a fold and thrust belt in which structure and timing of deformation can change significantly along strike on the scale a few hundred kilometers

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

measurements of martian dust devil winds with hirise 1 we report wind measurements within martian dust devils observed in plan view from the high resolution imaging science experiment hirise orbiting mars the central color swath of the hirise instrument has three separate charge coupled devices ccds and color filters that observe the surface in rapid cadence active features such as dust devils appear in motion when observed by this region of the instrument our image animations reveal clear circulatory motion within dust devils that is separate from their translational motion across the martian surface both manual and automated tracking of dust devil clouds reveal tangential winds that approach 20 30 m s 1 in some cases these winds are sufficient to induce a 1 decrease in atmospheric pressure within the dust devil core relative to ambient facilitating dust lifting by reducing the threshold wind speed for particle elevation finally radial velocity profiles constructed from our automated measurements test the rankine vortex model for dust devil structure our profiles successfully reveal the solid body rotation component in the interior but fail to conclusively illuminate the profile in the outer regions of the vortex one profile provides evidence for a velocity decrease as a function of r 1 2 instead of r 1 suggestive of surface friction effects however other profiles do not support this observation or do not contain enough measurements to produce meaningful insights

global context of the galileo e6 observations of jupiter s white ovals galileo solid state imaging ssi data taken during the e6 orbit on february 19 1997 offer a brief high resolution glimpse of jupiter s white ovals these data can be used to infer relative cloud heights and systematic rotations over a small area of latitude and longitude approximately 20 by 30 around the white ovals to fully understand the behavior of these cloud systems however a longer time span of global data is necessary in this paper we utilize ground based voyager and hubble space telescope data to interpret the galileo images we find that the white ovals translation rates have slowed from 0 39 deg day 1during the voyager era to 0 13 deg day 1in 1996 and they along with three smaller anticyclonic systems have coalesced into a system of alternating cyclonic and anticyclonic systems that has not been observed before the largest of the ovals bc is now impeding the eastward motion of the system causing more rapidly translating anticyclonic cells to catch the system and increase the westward extension of the equally spaced features rotational velocities for bc and a small anticyclonic system at 42 s have also been measured and peak at 120 m sec 1for both systems comparable to the mitchellet al j geophys res 86 8751 8757 measurements of bc and the great red spot grs from voyager data the motion of individual features and of the whole system in the ambient wind flow is discussed

the effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleums abstract the distributions of di and trimethylnaphthalenes in two sedimentary sequences from western australia have been examined by capillary gas chromatography and combined gas chromatography mass spectrometry a general decrease was observed in the relative proportions of dimethylnaphthalenes and trimethylnaphthalenes with increasing thermal maturity similar trends were also observed for six crude oils which have very different ratios of ethylcholestane epimers indicating very different thermal histories these results suggest that changes in the relative abundances of certain methyl substituted naphthalenes may be useful indicators of thermal maturity of sedimentary organic matter and the use of a number of isomer ratios is illustrated

bitumen ii from the paleoproterozoic here s your chance pb zn ag deposit implications for the analysis of depositional environment and thermal maturity of hydrothermally altered sediments abstract the formation of sedimentary exhalative sedex pb zn deposits is linked to ocean euxinia but recent evidence suggests that ferruginous conditions may have dominated the deep ocean during the middle proterozoic a maximum period for sedex distribution biomarkers of sulfate reducing and sulfide oxidising bacteria are valuable indicators of euxinic conditions in such settings organic matter om from sedex deposits is often affected by alteration and or migration but om entrapped within the kerogen mineral matrix bitumen ii may be less affected than the freely extractable om bitumen i we analysed bitumen ii from the paleoproterozoic here s your chance hyc pb zn ag deposit to find evidence of euxinic conditions in the depositional environment n alkane distributions in bitumen ii are markedly distinct from previously reported bitumen i bitumen ii contains long chain n alkanes up to c 36 or c 38 and a strong even over odd distribution in a number of samples which are 4 to 7 depleted in 13 c compared to n alkanes in bitumen i and verified as indigenous by comparison with 13 c of isolated kerogen these features are interpreted as evidence of sulfate reducing and sulfide oxidising bacteria confirming that hyc was deposited under euxinic conditions bitumen ii has the potential to reveal information from om that is degraded and or overprinted in bitumen i commonly used methylphenanthrene maturity ratios give conflicting information as to the relative maturity of bitumens i and ii bitumen i contains a far higher proportion of methylated phenanthrenes than bitumen ii as bitumen ii is sequestered within the kerogen mineral matrix it may have restricted access to the methyl pool of organic compounds that can donate methyl groups to aromatic hydrocarbons parameters that include both phenanthrene and methylphenanthrenes do not appear suitable to compare the maturity of bitumens i and ii hence there is no clear evidence that bitumen ii is of lower thermal maturity than bitumen i

identification and distribution of chrysene methylchrysenes and their isomers in crude oils and rock extracts abstract chrysene its methylated homologues and their structural isomers are important polyaromatic compounds in crudes oils coals and sediment extracts chrysene benzo a anthracene methylchrysenes and methylbenzo a anthracenes were unequivocally identified in mass chromatograms by comparison with authentic standards and by retention indices reported in the literature the response factors relating those of chrysene and methylchrysenes to internal standards perdeuterated chrysene chrysene d12 and pyrene pyrene d10 were obtained by gc ms analyses of mixture solutions with different concentration ratios the oil families of ordovician reservoirs in the cratonic region of the tarim basin nw china are distinguished by the distribution patterns of chrysene methylchrysenes and their isomers the majority of the oil accumulations and sediment extracts from the middle upper ordovician source rocks are characterized by low concentrations of benzo a anthracene and methylbenzo a anthracenes relative to chrysene and methylchrysenes respectively in contrast some oils with relatively high abundances of benzo a anthracene and methylbenzo a anthracenes were derived from cambrian and lower ordovician source rocks the effect of maturity on the distribution patterns of methylchrysenes in tertiary lacustrine shales from the liaohe basin east china was investigated the 2 1 methylchrysene ratio keeps a nearly constant value with increasing maturity at the low maturity stages and then it abruptly increases corresponding approximately to the onset of intense c 15 hydrocarbon generation this indicates that chrysene and its methylated homologues are useful molecular indicators in petroleum geochemistry

the evolving flow of jupiter s white ovals and adjacent cyclones abstract we present results regarding the dynamical meteorology of jupiter s white ovals at different points in their evolution starting from the era with three white ovals fa bc and de galileo continuing to the post merger epoch with only one oval ba cassini and finally to oval ba s current reddened state new horizons we demonstrate that the dynamics of their flow have similarly evolved along with their appearance in the galileo epoch oval de had an elliptical shape with peak zonal wind speeds of 90 m s 1 in both its northern and southern peripheries during the post merger epoch oval ba s shape was more triangular and less elliptical than oval de in addition to widening in the north south direction its northern periphery was 20 m s 1 slower and its southern periphery was 20 m s 1 faster than oval de s flow during the galileo era finally in the new horizons era the reddened oval ba had evolved back to a classical elliptical form the northern periphery of oval ba increased in speed by 20 m s 1 from cassini to new horizons ending up at a speed nearly identical to that of the northern periphery of oval de during galileo however the peak speeds along the southern rim of the newly formed oval ba were consistently faster than the corresponding speeds in oval de and they increased still further between cassini and new horizons ending up at 140 150 m s 1 relative vorticity maps of oval ba reveal a cyclonic ring surrounding its outer periphery similar to the ring present around the great red spot the cyclonic ring around oval ba in 2007 appears to be moderately stronger than observed in 1997 and 2001 suggesting that this may be associated with the coloration of the vortex the modest strengthening of the winds in oval ba the appearance of red aerosols and the appearance of a turbulent cyclonic feature to oval ba s northwest create a strong resemblance with the great red spot from both a dynamical and morphological perspective in addition to the white ovals we also measure the winds within two compact cyclonic regions one in the galileo data set and one in the cassini data set in the images these cyclonic features appear turbulent and filamentary but our wind field reveals that the flow manifests as a coherent high speed collar surrounding relatively quiescent interiors our relative vorticity maps show that the vorticity likewise concentrates in a collar near the outermost periphery unlike the white ovals which have peak relative vorticity magnitudes near the center of the vortex the cyclones contain several localized bright regions consistent with the characteristics of thunderstorms identified in other studies although less studied than their anticyclonic cousins these cyclones may offer crucial insights into the planet s cloud level energetics and dynamical meteorology

galileo imaging of jupiter s atmosphere the great red spot equatorial region and white ovals during the first six orbits of the galileo spacecraft s prime mission the solid state imaging ssi system acquired multispectral image mosaics of jupiter s great red spot an equatorial belt zone boundary a 5 m hot spot similar to the galileo probe entry site and two of the classic white ovals we present mosaics of each region approximating their appearance at visible wavelengths and showing cloud height and opacity variations the local wind field is derived by tracking cloud motions between multiple observations of each region with time separations of roughly 1 and 10 hr vertical cloud structure is derived in a companion paper by banfieldet al icarus135 230 250 galileo s brief high resolution observations complement earth based and voyager studies and offer local meteorological context for the galileo probe results our results show that the dynamics of the zonal jets and large vortices have changed little since voyager with a few exceptions we detect a cyclonic current within the center of the predominantly anticyclonic great red spot the zonal velocity difference between 0 s and 6 s has increased by 20 m sec 1 we measure a strong northeast flow approaching the hot spot this flow indicates either massive horizontal convergence or the presence of a large anticyclonic vortex southeast of the hot spot the current compact arrangement of two white ovals and a cyclonic structure greatly perturbs the zonal jets in that region

novel aromatic hydrocarbons of probable bacterial origin in a jurassic lacustrine sequence novel series of aromatic hydrocarbons apparently bacterially derived were detected by gc ms analysis of an oil and three samples of its source rock in addition to high levels of known bacterial marker compounds hopanes benzohopanes and d ring monoaromatic 8 14 secohopanoids all samples exhibited a new series of aromatic secohopanoids which appeared to comprise pairs of c28 c31 demethylated counterparts of the regular d ring monoaromatic 8 14 secohopanoids lacking either the c 27 or more probably the c 28 methyl group further new series appeared to be composed of c28 c30 analogues of the regular and demethylated monoaromatic secohopanoids with an additional c c bond in the e ring alkylnapthalene distributions in the rock samples were dominated by 1 1 5 6 tetramethyl 1 2 3 4 tetrahydronaphthalene 1 2 5 trimethylnapthalene and 1 2 5 6 tetramethylnapthalene deriving from degradation of aromatic 8 14 secohopanoids three prominent phenanthrene analogues of these napthalene derivatives appeared to be present exhibiting similar relative abundance trends in the rock samples which suggests common bacterially derived precursors

biomarkers reveal the role of photic zone euxinia in exceptional fossil preservation an organic geochemical perspective photic zone euxinia pze has proven important for elucidating biogeochemical changes that occur during oceanic anoxic events including mass extinction and conditions associated with unique fossil preservation organic geochemical analyses of a 380 ma invertebrate fossil which included well preserved soft tissues from the gogo formation canning basin western australia showed biomarkers and stable isotopic values characteristic of pze and a consortium of sulfate reducing bacteria which lead to exceptional fossil and biomarker preservation the carbonate concretion contained phytoplankton green sulfur bacteria chlorobi and sulfate reducing bacteria biomarkers with an increasing concentration toward the nucleus where the fossil is preserved the spatial distribution of cholestane unequivocally associated with the fossilized tissue and its high relative abundance to the total steranes suggest that the fossil is a crustacean the presence of an active sulfur cycle in this devonian system including sulfate reduction and the resulting pze played a pivotal role in the preservation of soft tissue from the fossil and its associated low maturity biomarker ratios

spherical shell tectonics effects of sphericity and inextensibility on the geometry of the descending lithosphere the shape of a deep seismic zone is thought to represent that of the descending slab of lithosphere the lithosphere before subduction is a spherical shell and the shape of the descending slab is the result of the deformation of the spherical lithosphere at the subduction zone upon bending a spherical shell often deforms in a very different way from a simple plate we examine whether the actual shape of the descending slab can be explained by a simple bending of an inextensible spherical shell which shows little surface deformation under moderate stress this examination is made region by region for most of the subduction zones in the world by means of an analogue method the lithosphere is simulated by an inextensible spherical shell made of polyvinyl chloride resin the wadati benioff zone is shaped by plaster by referring to the reliable hypocentral data selected from the international seismological centre isc bulletins the spherical shell is forced to fit the miniature of the wadati benioff zone fitting is first attempted only by bending if a good fit is not attainable and if a discontinuity or gap in seismic activity is observed in the relevant region the spherical shell is torn along this discontinuity or gap and the goodness of fit is reexamined the results of the analysis are summarized as follows 1 the shape of the wadati benioff zone can be simulated largely by a simple bending of a spherical shell without surface deformation 2 in almost all of the regions of poor fit with bending a good fit can be achieved by tearing the spherical shell along the trace of low seismicity the sphericity of the lithosphere and the inextensibility upon deformation are the two essential factors in controlling the slab shape this means that the lateral constraint is most important for understanding the geometry of the downgoing slab of lithosphere and the stress state within it further several problems related to the deformational characteristics of the spherical lithosphere are also reviewed and discussed in connection with subduction tectonics

geochemical characterization of malm zeta laminated carbonates from the franconian alb sw germany ii abstract during jurassic times especially within the malm stage local depressions formed on the eastern bavarian carbonate platform that were surrounded by wall reefs this created a unique depositional environment where in an open marine setting stagnant and anoxic bottom waters developed in an intra reef depression anoxic conditions were stabilized below wave base by enhanced salinity in the bottom waters and establishment of a density stratification biomarker analysis was applied to characterize palaeosalinity and redox conditions utilizing organic sulfur compound methylated chroman hopanoid and saturated isoprenoid distributions prevention of terrigenous influx by protecting reef walls lead to iron deficiency in intra reefal sediments causing early diagenetic sulfurization of functionalized lipids absence of clay mineral catalysts and early sulfurization favored an unusual steroid distribution lacking rearranged analogues but providing coexistence of saturated steranes with and configuration 13 17 spirosterenes unknown sterenes and steradienes as well as mono di and triaromatic steroids desulfurization of the polar fraction was carried out for two samples to verify that palaeoenvironment reconstruction based on free hydrocarbon and heterocompound distribution was not invalidated by sulfur quenching of selected compounds gammacerane was found to be the only component to occur exclusively in the sulfur bound fraction only minor amounts of hydrocarbons were released upon desulfurization implying that free bitumen analysis was applicable for organofacies characterization organic petrological investigation of organic mats revealed the presence of two different types of such structures comparison of organoclast fluorescence spectra with those of extracted porphyrin fractions indicate an origin of porphyrins exclusively from cyanobacterial mats whereas algal dominated mats yield no porphyrins this aims towards a better localization of specific biomarker origin in geological samples

formation of holocene sedimentary laminae in the black sea and the role of the benthic flocculent layer holocene black sea sediments recovered in 1988 and 1993 from box cores and gravity cores were analyzed geochemically microscopically and with backscattered electron imagery bsei in order to determine the temporal geochemical and sedimentological relationships between the benthic flocculent layer often referred to as the fluff layer and the formation of underlying laminated unit i sediments existence of a permanent benthic fluff layer in the black sea basin is suggested acting as a geochemical transition layer within which all sedimentary particles are hydraulically sorted and particles subject to dissolution or organic remineralization are altered prior to accumulation we propose that particle residence time within the benthic fluff layer is a key factor in determining sedimentary microfabric and geochemical composition of laminated unit i sediments we present a schematic model depicting the above relationships and use it to propose a paleoflux scenario for laminae formation in the unit ii sapropel

dynamical implications of jupiter s tropospheric ammonia abundance abstract groundbased radio observations indicate that jupiter s ammonia is globally depleted from 0 6 bars to at least 4 6 bars relative to the deep abundance of 3 times solar a fact that has so far defied explanation the observations also indicate that i the depletion is greater in belts than zones and ii the greatest depletion occurs within jupiter s local 5 m hot spots which have recently been detected at radio wavelengths here we first show that both the global depletion and its belt zone variation can be explained by a simple model for the interaction of moist convection with jupiter s cloud layer circulation if the global depletion is dynamical in origin then important endmember models for the belt zone circulation can be ruled out next we show that the radio observations of jupiter s 5 m hot spots imply that the equatorial wave inferred to cause hot spots induces vertical parcel oscillation of a factor of 2 in pressure near the 2 bar level which places important constraints on hot spot dynamics finally using spatially resolved radio maps we demonstrate that low latitude features exceeding 4000 km diameter such as the equatorial plumes and large vortices are also depleted in ammonia from 0 6 bars to at least 2 bars relative to the deep abundance of 3 times solar if any low latitude features exist that contain 3 times solar ammonia up to the 0 6 bar ammonia condensation level they must have diameters less than 4000 km

back arc thrusting in the eastern sunda arc indonesia a consequence of arc continent collision the structure of the eastern sunda back arc region is dominated by two large north directed thrusts the wetar and flores thrusts and one or more minor thrusts which may represent early stages of subduction polarity reversal of the arc the relationships between thrusting and magmatic activity surface slopes cross arc faulting uplift forearc structure and collision by the australian continental margin provide constraints on the likely driving mechanisms of thrust formation driving mechanisms are considered in two broad categories one set of possible mechanisms originates within the upper plate and includes gravity sliding gravity spreading and magmatic intrusion the other set focuses on stress propagation between the upper and lower plates and for this arc system the major mechanism is that of continental collision while no one mechanism explains the range of observations we see in the back arc region all of these aspects play some role in the development of the thrusts we can eliminate upper plate mechanisms as primary driving forces because slope effects are similar in areas of both thrusting and nonthrusting in addition the wetar thrust shows a negative relation between thrusting and volcanism and side looking airborn radar images show no evidence of postvolcanic rifting that could accompany intrusion without volcanism collision between the arc and the australian continent provides the clearest driving mechanism but it does not explain the discontinuous nature or the particular location of the thrusts we suggest a sequence that appears to account for the data and to provide insight into the controversies often associated with other such thrust belts thrusting was initiated in those areas where the crust of the forearc region was thick a factor that facilitated stress propagation across the arc and where the crust of the back arc was thin which facilitated back arc thrusting thrusting concentrated at the base of the slope where the slope stress is maximum the early thrusting may have been helped also by thermal weakening of the crust due to volcanism as convergence proceeded volcanism waned then ceased in the eastern part of the arc the crust then strengthened and thrusting required higher stress to maintain and propagate this later stage should show higher seismic energy release which appears to be the case for the wetar thrust region displacement on the flores thrust appears to be matched by deflection of the volcanic arc we have estimated shortening in the back arc from interpretation of reflection profiles and for the flores thrust the value of approximately 30 km is consistent with that estimated for deflection of the arc compressional deformation continues west of the collision zone across the bali basin and into java it is reported in ne sumatra as well this deformation involves much less convergence than the eastern sunda thrusts and it may be related to magmatic processes to subduction of oceanic plateaus such as the roo rise or in the case of the bali basin to efficient lateral propagation of the flores thrust

wave enhanced sediment gravity flows and mud dispersal across continental shelves reappraising sediment transport processes operating in ancient mudstone successions recent studies of marine shelf sediment dispersal show that wave enhanced sediment gravity flows are widespread phenomena and can transport large volumes of fluid mud rapidly across low gradient shelves flow evolution is controlled by sediment supply seabed gradient and spatial distribution of wave energy at the seabed using existing flow models we predict that such flows in mud dominated sediments will develop a three part microstratigraphy produced by changing flow conditions beginning with wave induced turbulent resuspension then development of a wave enhanced sediment gravity flow prior to lutocline collapse and suspension settling petrographic examination of modern flow deposits collected from the eel shelf reveals that resultant beds possess a microstratigraphy consistent with our hypothesis a silt rich basal subunit with curved ripple laminae abruptly overlain by a subunit composed of continuous intercalated silt clay laminae and an upper clay rich drape analyses of beds from ancient mud rich outer shelf and basinal successions cleveland ironstone jurassic uk and mowry shale cretaceous united states show that they too contain beds with this three part organization suggesting that such flows were active in these ancient settings too recognition of these microstructures in these ancient mud dominated successions demonstrates that sediment in these settings was commonly reworked and transported advectively downslope by high energy events contrasting with previous interpretations of these units that deposition was dominated by quiescent suspension settling identification of these recognition criteria now allows the products of this newly recognized sediment dispersal mechanism to be identified in other shale dominated successions

seismicity maps of the indonesian region as a continuation of our paper on the seismicity maps of the new guinea solomon island region we now discuss the indonesian arc maps of tectonic flux are presented as follows 1 1 on the basis of the data of all registered tectonic earthquakes that took place along the arc from 103 e to 135 e between 1953 01 01 and 1970 12 31 in this category three maps have been prepared 1 1 a for shallow depths h 100 km 1 2 b for the intermediate and deep class h 100 km and 1 3 c for all shocks regardless of their focal depth h 0 km 2 2 a general map has also been constructed for all earthquakes for which m 7 0 data was considered from shocks which occurred from 1897 01 01 to 1977 12 31 in the area bounded in the west by longitude 90 e in the east by meridian 148 e in the north by latitude 12 n and in the south by latitude 16 s respectively a total of 224 earthquakes were taken into account in addition to these using the data of the shocks belonging to category 1 a depth contour map of the upper surface of the downgoing oceanic lithosphere has been created so far as this can be estimated by the spatial distribution of earthquake foci benioff zone

geochemistry of an early diagenetic concretion from the birchi bed l lias w dorset u k abstract three concentric growth zones calcitic core dolomitic zone outer rim have been recognised in a carbonate concretion from the birchi bed l lias u k of w dorset each zone has characteristic trace metals carbonate stable isotopes and biological markers the organic matter which fuelled the formation of the concretion was derived from the immature parent shales with beef however bitumen trapped within each zone has been affected by the dominant bacterial processes which led to the precipitation of the carbonates it is suggested that the calcitic core precipitated under sulphate reducing conditions here most biological markers are present in low amounts possibly as a result of bacterial degradation the dolomitic zone is characterised by a high abundance of isotopically light phytane which suggests direct input from methanogens this is consistent with isotopic data for the dolomite which indicates a dominantly methanogenic origin however the presence of hop 17 21 ene n alkenoic acids and of the c 32 hopanoic acid indicate concomitant non methanogenic bacterial activity in the outer rim where calcites have negative carbon isotopic values the high concentrations of n alkenoic acids in the bitumen suggest a non methanogenic bacterial origin for the carbonate the study shows the potential of using organic geochemical techniques to study the in situ formation of diagenetic precipitates biological markers trapped in the concretion may provide a snapshot of sedimentary microbial processes

color and the vertical structure in jupiter s belts zones and weather systems abstract radiative transfer analysis was performed with data taken by the galileo spacecraft solid state imager ssi during its nominal mission december 1995 to december 1997 the objective is to use the methane band 727 and 889 nm and color 410 and 756 nm sensitivities to identify the vertical position of cloud absorption that leads to coloration earlier work banfield et al 1998 icarus 135 230 250 with only the near ir continuum and methane band images yielded information about the vertical distribution of cloud scatterers but no information on the wavelength dependence of cloud absorption the new analysis employs the same parameter retrieval algorithm but adds the 410 nm wavelength under the assumption that the 410 nm absorption by cloud particles is indicative of spectrally broad blue absorption the new channel gives color information the primary color difference between the dark north equatorial belt neb and the brighter equatorial zone ez appears to be in the tropospheric haze layer s 410 nm single scattering albedo this layer extends through the stably stratified region approximately from 200 to 800 mbars the base of the haze layer is slightly deeper in the neb by about 200 mbars than in the ez and a variable thickness white cloud layer at the base of the haze exists in both regions but is about five times optically thicker in the ez within the ez slight color variation is seen with latitude again due to 410 nm single scattering albedo variation in the haze layer anomalous regions such as the great red spot and a 5 m hot spot are modeled showing additional variations in the structure and color of the tropospheric haze deeper clouds with pressures of 1 7 bars are seen in occasional clearings but their opacity and color are not well constrained by the data

carbon isotopic compositions of prokaryotic lipids as tracers of carbon cycling in diverse settings recent work has highlighted the ubiquity of bacteria and archaea and continues to affirm their significance in diverse biogeochemical processes the 13c values and distributions of diagnostic lipids derived from such microorganisms can provide insights into prokaryotic processes in modern settings and are one of the few means by which past prokaryotic processes in depositional settings can be elucidated here we present a brief review of prokaryotic lipids commonly observed in sediments and the controls on their carbon isotopic compositions we then present two case studies one of mediterranean cold seeps at which anaerobic oxidation of methane occurs and one of a holocene peat deposit in which a variety of aerobic and anaerobic microorganisms govern the degradation of organic matter these two studies illustrate the potential utility of compound specific carbon isotope analyses to deconvolute pathways of carbon flow in microbial communities

lacustrine source rock deposition in response to co evolution of environments and organisms controlled by tectonic subsidence and climate bohai bay basin china three paleogene syn rift intervals from the bohai bay basin the most petroliferous basin in china were analyzed with sedimentological and geochemical techniques to characterize the lateral source rock heterogeneities to reveal the environmental and ecological changes through geologic time and to construct depositional models for lacustrine source rocks under different tectonic and climatic conditions the third es3 and first es1 members of the eocene shahejie formation and the oligocene dongying formation ed display widely variable total organic carbon contents hydrogen indices and visual kerogen compositions suggesting changes in organic facies from deep to marginal sediments carefully selected deep lake facies samples from any interval however display fairly uniform biomarker composition these three intervals have distinctly different biomarker assemblages which indicate weakly alkaline freshwater lakes with a moderately deep thermocline during es3 deposition alkaline saline lakes with shallow chemocline during es1 deposition and acidic freshwater lakes with deep unstable thermocline during the deposition of the dongying formation such environmental changes corresponded to changes in subsidence rate and paleoclimate from rapid subsidence and wet climate during es3 deposition through slow subsidence and arid climate during es1 deposition to rapid subsidence and wet climate during ed deposition and resulted in synchronous changes in terrigenous organic matter input phytoplankton community and primary productivity the co evolution of environments and organisms controlled by tectonic subsidence and climate accounted for the deposition and distribution of high quality lacustrine source rocks with distinctly different geochemical characteristics most rift basins experienced changes in subsidence rates and possibly changes in climates during their syn rift evolutions the models constructed in this paper may have important implications for source rock prediction in other lacustrine rift basins

sulfur rich petroleum derived from lacustrine carbonate source rocks in bohai bay basin east china abstract crude oils produced from the zhanhua depression bohai bay basin are high in sulfur and differ from most lacustrine oils in this basin and elsewhere physical properties biomarker ratios and aromatic hydrocarbon assemblages reveal that they are derived from carbonate source rock horizons representative source rock samples with abundant organic matter toc 1 and s 2 5 mg hc g rock were selected for further correlation and their high bitumen contents indicated their indigenousness to saline or carbonate depositional environments the results of oil source rock correlation suggest that these sulfur rich heavy oils originate from es 3 4 carbonates and marls limited to the bonan sag maturity assessments with burial history showed that they were expelled at the early oil generation window high levels of 20s 5 14 17 and 5 14 17 steranes together with low values for the ts ts tm ratio and two methylated aromatic ratios mdr and mpi 1 were observed in these oils sulfur associated with evaporite and carbonate environments is a significant factor not only in controlling the occurrence of biomarker isomers but also for petroleum formation at abnormally low thermal stress levels

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

biomarker distributions in crude oils and source rocks from different sedimentary environments abstract the saturated and aromatic hydrocarbons from a significant number of oils and source rocks derived from terrestrial and marine organic matter have been analysed by gc and gc ms results show that certain classes of biomarkers including bicyclic sesquiterpanes tricyclic terpanes pregnanes methylsteranes rearranged steranes hopane sulfides benzohopanes long chain alkylbenzenes and pentacyclic triterpanes can be used to distinguish differences in source input and or depositional environments variations in the distributions of the naphthalenes phenanthrenes fluorenes dibenzofurans dibenzothiophenes naphthobenzothiophenes and triaromatic steroid hydrocarbons may also reflect disparities in source input or sedimentary environments

compound specific stable carbon isotope analysis as a tool for correlating coal sourced oils and interbedded shale sourced oils in coal measures an example from turpan basin north western china molecular geochemical methods have shown that it is often diacult to diaerentiate between coal and interbedded shale sourced oils even though coals and interbedded shales may exhibit considerable organic influx variation e g land plant vs algal organic matter due to the changes of depositional setting however compound specific stable carbon isotopic compositions are sensitive to the source input variations typically specific molecules are more depleted in 13 c with increasing content of aqueous biota this hypothesis is examined and exemplified by comparing the stable carbon isotopic ratios of n alkanes from source rock extracts and related oils of the turpan basin northwestern china stable carbon isotopic values of n alkanes extracted from coals and interbedded shales show that d 13 c values of n alkanes with less than 20 carbon atoms vary only slightly however there are dramatic changes in the isotopic compositions of higher molecular weight n alkanes furthermore n alkanes from coal extracts are enriched in 13 c relative to that of interbedded shales with excursions up to 2 3 this comparison enables the diaerentiation of coal and interbedded shale sourced oils and provides information useful in assessing the hydrocarbon system of a basin 2000 elsevier science ltd all rights reserved

molecular indicators of palaeoenvironmental conditions in an immature permian shale kupferschiefer lower rhine basin north west germany from free and s bound lipids a study of the distributions of free and s bound biomarkers and their 13c values in the extract of a bulk sample of the permian kupferschiefer from the lower rhine basin has been carried out to provide a more detailed characterization of the biological inputs the distributions and isotopic compositions of selected components released from nickel boride desulphurization have been compared with those of components in the free fraction the free biomarkers occur in greater abundance than their s bound counterparts the distribution and carbon isotopic composition of both free and bound components in the extract indicate a major cyanobacterial and algal input likewise the free and bound aromatic hydrocarbons contain components which reveal an origin from the carotenoids of chlorobiaceae green sulphur bacteria providing molecular evidence for the occurrence of photic zone anoxia in the water column most of the components in the complex mixture of mono di tri and tetra aromatics in the free aromatic hydrocarbon fraction result from cyclization and aromatization reactions

the role of algal blooms in the formation of lacustrine petroleum source rocks evidence from jiyang depression bohai gulf rift basin eastern china abstract algal blooms are responsible for the laminae in the lacustrine shahejie formation in the jiyang depression one of the sub basins of the bohai gulf rift basin in eastern china about 65 oil fields have been discovered in this depression during the past 40 years and the oil is mainly derived from three types of finely laminated lacustrine rocks of shahejie formation eocene oligocene these lacustrine petroleum source rocks are oil shales calcareous shales and calcareous laminated mudstones optical sem and bsei analyses of these source rocks reveal that there are algal coccoliths and dinoflagellates laminae in the rocks the individual algal lamina is generally composed almost wholly of one species such as reticulofenestra bohaiensis in coccolith laminae and fromea as well as bohaidina in dinoflagellate laminae this distribution suggests that the algal laminae formed from algal blooms in the ancient lake other components of source rocks included organic matter laminae carbonate laminae and clay rich laminae we also discuss the sedimentation of organic matter laminae and carbonate laminae which were related to algal blooms we conclude that the laminated lacustrine petroleum source sediment of jiyang depression formed during episodes of algal blooms alternating with chemical and detrital sedimentation and this represents the primary mechanism responsible for the formation of lacustrine petroleum source rocks

mineralogical and chemical distribution of the es3l oil shale in the jiyang depression bohai bay basin e china implications for paleoenvironmental reconstruction and organic matter accumulation abstract the es3l lower sub member of the third member of the eocene shahejie formation shale in the jiyang depression is a set of relatively thick and widely deposited lacustrine sediments with elevated organic carbon and is considered to be one of the most important source rocks in east china we can determine the mineralogy organic and inorganic geochemistry of the es3l shale and calculate paleoclimate indexes by using multiple geochemical proxies based on organic chemistry total organic carbon toc and rock eval pyrolysis major and trace elements x ray diffraction and carbon and oxygen isotope data from key wells alongside ecs elemental capture spectroscopy well log data these indicators can be used to analyze the evolution of the paleoenvironment and provide a mechanism of organic matter om accumulation the es3l oil shale has high toc abundance most samples 3 0 and is dominated by type i kerogens additionally the organic rich shale is rich in cao and enrichment in some trace metals is present such as sr ba and u the positive 13c and negative 18o values high sr ba b ga and ca ca fe ratios and low c s ratios indicate that the es3l shales were mainly deposited in a semi closed freshwater brackish water lacustrine environment the consistently low ti al and si al ratios reflect a restricted but rather homogeneous nature for the detrital supply many redox indicators including the th u v v ni and u ratios pyrite morphology and toc ts fe diagrams suggest deposition under dysoxic to suboxic conditions subsequently the brackish saline bottom water evolved into an anoxic water body under a relatively arid environment during which organic lean marls were deposited in the early stage later an enhanced warm humid climate provided an abundant mineral nutrient supply and promoted the accumulation of algal material om input from algal blooms reached a maximum during the deposition of the organic rich calcareous shale with seasonal laminations high p ti ratios and a strongly positive relationship between the p and toc contents indicate that om accumulation in the oil shale was mainly controlled by the high primary productivity of surface waters with help from a less stratified water column factors such as the physical protection of clay minerals and the dilution of detrital influx show less influence on om enrichment

on the interaction of jupiter s great red spot and zonal jet streams abstract in this paper jupiter s great red spot grs is used to determine properties of the jovian atmosphere that cannot otherwise be found these properties include the potential vorticity of the grs and its neighboring jet streams the shear imposed on the grs by the jet streams and the vertical entropy gradient i e rossby deformation radius the cloud cover of the grs which is often used to define the grs s area and aspect ratio is found to differ significantly from the region of the grs s potential vorticity anomaly the westward going jet stream to the north of the grs and the eastward going jet stream to its south are each found to have a large potential vorticity jump the jumps have opposite signs and as a consequence of their interaction with the grs the shear imposed on the grs is reduced the aspect ratio of the grs s potential vorticity anomaly depends on the ratio of the imposed shear to the strength of the anomaly the east west to north south aspect ratio is found to be 2 1

organic geochemistry of the early toarcian oceanic anoxic event in hawsker bottoms yorkshire england a comprehensive organic geochemical investigation of the hawsker bottoms outcrop section in yorkshire england has provided new insights about environmental conditions leading into and during the toarcian oceanic anoxic event t oae 183 ma rock eval and molecular analyses demonstrate that the section is uniformly within the early oil window hydrogen index hi organic petrography polycyclic aromatic hydrocarbon pah distributions and tricyclic terpane ratios mark a shift to a lower relative abundance of terrigenous organic matter supplied to the sampling locality during the onset of the t oae and across a lithological transition unlike other ancient intervals of anoxia and extinction biomarker indices of planktonic community structure do not display major changes or anomalous values depositional environment and redox indicators support a shift towards more reducing conditions in the sediment porewaters and the development of a seasonally stratified water column during the t oae in addition to carotenoid biomarkers for green sulfur bacteria gsb we report the first occurrence of okenane a marker of purple sulfur bacteria psb in marine samples younger than 1 64 ga based on modern observations a planktonic source of okenane s precursor okenone would require extremely shallow photic zone euxinia pze and a highly restricted depositional environment however due to coastal vertical mixing the lack of planktonic okenone production in modern marine sulfidic environments and building evidence of okenone production in mat dwelling chromatiaceae we propose a sedimentary source of okenone as an alternative lastly we report the first parallel compound specific c13 record in marine and terrestrial derived biomarkers across the t oae the c13 records of short chain n alkanes acyclic isoprenoids and long chain n alkanes all encode negative carbon isotope excursions cies and together they support an injection of isotopically light carbon that impacted both the atmospheric and marine carbon reservoirs to date molecular c13 records of the t oae display a negative cie that is smaller in magnitude compared to the bulk organic c13 excursion although multiple mechanisms could explain this observation our molecular petrographic and rock eval data suggest that variable mixing of terrigenous and marine organic matter is an important factor affecting the bulk organic c13 records of the t oae

vertical wind shear on jupiter from cassini images 1 multifilter images of jupiter acquired by the cassini imaging science subsystem iss are used to derive zonal winds at altitudes above and below the visible cloud deck small features unique to the ultraviolet images of iss are tracked to get the systematic high altitude zonal winds comparison between the zonal winds from ultraviolet images and the vertical profile of zonal winds from the cassini composite infrared spectrometer cirs shows that the zonal winds from the ultraviolet images are from a pressure level that is 0 2 scale heights higher than the pressure level of the zonal winds from continuum band images deeper zonal winds at different latitudes of the equatorial region are measured by tracking cloud features observed within hot spots on continuum band images the deeper zonal winds in this study extend the measurement of the galileo probe to different latitudes of the equatorial region comparison between the galileo probe and this study suggests that these fast moving clouds within hot spots are deeper than 3 bars and are therefore probably water clouds

life cycles of spots on jupiter from cassini images using the sequence of 70 day continuum band 751 nm images from the cassini imaging science system iss we record over 500 compact oval spots and study their relation to the large scale motions the 100 spots whose vorticity could be measured the large spots in most cases were all anticyclonic we exclude cyclonic features chaotic regions because they do not have a compact oval shape but we do record their interactions with spots we distinguish probable convective storms from other spots because they appear suddenly grow rapidly and are much brighter than their surroundings the distribution of lifetimes for spots that appeared and disappeared during the 70 day period follows a decaying exponential with time constant mean lifetime of 3 5 days for probable convective storms and 16 8 days for all other spots extrapolating the exponential beyond 70 days seriously underestimates the number of spots that existed for the entire 70 day period this and other evidences size shape distribution in latitude suggest that these long lived spots with lifetime larger than 70 days are from a separate population the zonal wind profile obtained manually by tracking individual features this study agrees with that obtained automatically by correlating brightness variations in narrow latitude bands porco et al 2003 some westward jets have developed more curvature and some have developed less curvature since voyager times but the number of westward jets that violate the barotropic stability criterion is about the same in the northern hemisphere the number of spots is greatest at the latitudes of the westward jets which are the most unstable regions according to the barotropic stability criterion during the 70 day observation period the great red spot grs absorbed nine westward moving spots that originated in the south equatorial belt seb where most of the probable convective storms originate although the probable convective storms do not directly transform themselves into westward moving spots their common origin in the seb suggests that moist convection and the westward jet compose a system that has maintained the grs over its long lifetime

seismotectonics of the central segment of the indonesian arc abstract in this paper a revision of seismicity affecting the central segment of the indonesian island arc ranging between 110 and 126 e is presented using the areal and in depth distribution of seismic activity strain release maps and focal mechanisms lateral changes in the wadati benioff zone have been analyzed to determine possible boundaries between portions of lithosphere with different subduction geometries the seismicity pattern indicates that the sumbawa flores wetar sector shows different forms of behaviour with respect to the adjacent sectors these include driving mechanism inclination and continuity of the subducting slab and subduction features this area therefore seems to be isolated from the sunda and banda arcs by two principal boundaries these having a nearly n s trend in the bali region and with a nearly e w trend in the region ranging between wetar northern timor and tanibar the first boundary characterized by an absolute minimum of seismic activity at all ranges of depth has been interpreted in terms of subduction of the roo rise aseismic bathymetric ridge for the second boundary dividing a northwardly steeply dipping slab from an e w subducting slab dipping with an angle of 30 40 a tear in the upper part depth less than 300 km and a hinge fault system in the deepest part of the lithosphere have been proposed from the analysis of focal mechanisms of shallow earthquakes it was inferred that the central part of the indonesian arc is subject to a vortex shaped stress field centred on the savu basin in this model the compressive axes appear to rotate counterclockwise from sw to nne in the sumba sumbawa western flores region and clockwise from w to nnw in the timor eastern flores zone to interpret these features on the basis of seismological evidence a lateral discontinuity in the arc trench system close to sumba a collision between sumba and sumbawa and a rotation towards the north northeast of sumba have been suggested the proposed structural discontinuity trending nw se may represent a major transcurrent fault zone through which the australian continental lithosphere comes into contact with the indian oceanic lithosphere

a comparative study of jovian cyclonic features from a six year 1994 2000 survey abstract this work presents a six year study aimed at characterizing the morphology and properties of the atmospheric features present in jovian cyclonic regions it complements our previous analysis for the same period on the anticyclonic vortices morales juberias et al 2002 icarus 157 76 90 the main difference between cyclonic and anticyclonic regions in jupiter is that a variety of organized morphologies are present in the cyclonic areas although they can be grouped consistently into five different types filamentary turbulence related to the highest speed jets organized folded filamentary regions elongated areas with contours closed by a ribbon like feature discrete closed brown cyclones barges and peculiar transient structures such as short wave trains and cyclonic cells we present data on their color contrast size aspect ratio distribution lifetimes relation to the jet system and to the anticyclones and motions global and internal to the features most cyclonic features show a rapid evolution compared to the anticyclones and tend to be dispersed zonally although some survive for a few years we used the barges that are the most representative long lived and extended type of cyclonic features to show that there exists a linear relationship between their relative velocity and the mean zonal flow speed similar to that found in our previous work on the anticyclones there is also some evidence that the drift rate of barges is related to the planetary minus flow vorticity gradient

palaeoenvironmental conditions during deposition of the upper cretaceous oil shale sequences in the songliao basin ne china implications from geochemical analysis abstract excellent hydrocarbon source rocks oil shales containing type i organic matter om were deposited in the continental songliao rift basin during the late cretaceous a major contribution of aquatic organisms dinoflagellates green algae botryococcus and minor input from macrophytes and land plants to om accumulation is indicated by n alkane distribution steroid composition and 13 c values of individual biomarkers microbial communities included heterotrophic bacteria cyanobacteria and chemoautotrophic bacteria as well as purple and green sulfur bacteria the presence of methanotrophic bacteria is indicated by 13 c depleted methyl hopane the sediments were deposited in a eutrophic alkaline palaeolake highly reducing saline bottom water conditions and a stratified water column existed during om accumulation of the qingshankou formation and member 1 of the nenjiang formation this is indicated by low pristane phytane gammacerane index and mttc ratios and the presence of carotane and aryl isoprenoids however an abrupt change in environmental conditions during deposition of member 2 of the nenjiang formation is indicated by significant changes in salinity and redox sensitive biomarker ratios a freshwater environment and suboxic conditions in the deep water prevailed during this period higher input of terrigenous om occurred during deposition of the upper nenjiang formation good oil to source rock correlation was obtained using biomarker fingerprints of oil stained sandstone from the quantou formation and oil shales from the qingshankou formation based on the extent of isomerisation of c 31 hopanes the oil was most probably derived from oil shales of the qingshankou formation in deeper parts of the basin

oscillations and velocity structure of a long lived cyclonic spot dark brown cyclonic spots barges at 14 n were studied by using voyager 1 and 2 images of jupiter movie sequences were made to study the spots behavior over intervals of 50 days and longer these movies revealed that the length and width vary by 9 with a period of about 15 days while the area remains approximately constant the horizontal velocity field was investigated for an interval of about 1 day flow around the largest barge feature 6 occurs as a ring current the vorticity inferred is about 2 times that of the ambient cyclonic zonal circulation and about one half the value of the local planetary vorticity length and width variations appear to be associated with a nonzero horizontal divergence field if the oscillations are a natural mode of the system the 15 day period will provide an important datum for testing models of stable closed vortices

possible algal origin of long chain odd n alkanes in immature sediments as revealed by distributions and carbon isotope ratios a pliocene oil shale pula hungary a c3 plant triticum aestivum and a c4 plant zea mays were compared using isotopic composition of bulk organic matter along with distributions and individual carbon isotope ratios of n alkanes from organic extracts the microalga botryococcus braunii a race was thus shown to be the main source of the predominant 27 29 and 31 n alkanes of pula sediment therefore the dominance of odd carbon numbered n alkanes in the range c25 35 in extracts from immature sediments shall not be systematically assigned to higher plant contribution but algal input is also possible in fact the long chain n alkanes with an odd predominance previously observed in extracts of various immature sediments are likely to be derived at least partially from algae

deep seismicity and modes of deformation in tonga subduction zone the geometry of deep 400 km earthquakes in the subducting western edge of the pacific plate when related to the local distribution of seismic activity reveals a complex pattern of planes of shear failure enabling the modes of deformation by which the descending plate shortens and thickens to be identified the deepest part of the slab is displaced laterally suggesting that it fails to penetrate the discontinuity at 670 km

higher plant biomarkers reflect palaeovegetation changes during jurassic times abstract the relative abundances of three higher plant derived biomarkers retene cadalene and ip ihmn have been measured in marine sedimentary rocks from the northwest margin of australia it is thought that each biomarker represents input from a different plant type the distributions of these three compounds form a fingerprint representing higher plant input hpf variations in hpf in oxfordian sediments were nearly identical in all three locations with retene becoming very abundant relative to the other two compounds with decreasing age of the sediment this finding strongly suggests that the composition of terrestrial input during deposition largely determines hpf and that the possible effects of diagenesis and catagenesis on the distribution of the three biomarkers are relatively unimportant the marked increase in the abundance of retene relative to that of cadalene during the oxfordian is interpreted to reflect an increase in the contribution of plants that produced precursors for retene i e conifers brought about by a significant change in climate this was exemplified by measuring the distributions of retene and cadalene expressed in the higher plant parameter hpp for a suite of sediments from the carnarvon basin western australia covering the complete jurassic period the hpp profile displays three major cycles each covering a period of at least 10 million years this profile not only compared well with published palaeoclimate data but also showed a remarkable similarity with second order cycles in the global sea level curve thus strongly supporting the proposal that variations in hpf and hpp are indications of changes in palaeoclimate the relation with global sea level further suggests that global factors e g the atmospheric carbon dioxide concentration may play a major role in determining the observed variations in the distributions of these higher plant derived biomarkers

records of seasonal flux in holocene laminated sediments gulf of california holocene laminated sediments from guaymas basin gulf of california mexico have in the past been described as annual couplets of sedimentation couplets comprise an alternation of diatom and terrigenous rich sediment reflecting winter and summer flux to the sediment respectively new data from backscattered electron imagery bsei show that a three component pattern of sedimentation is preserved comprising 1 a lithogenic lamina consisting of clays silt and minor diatomaceous material deposited during the summer and autumn wet season 2 a mixed flora diatomaceous lamina deposited during the early winter collapse of the thermocline and onset of water column mixing and 3 a near monospecific flora lamina of chaetoceros resting spores or more rarely skeletonema costatum representing deposition from or at the end of the spring coastal upwelling bloom recent sediment trap biogenic and terrigenous flux data also show three to four major flux events per year direct comparisons are possible between bsei records and recent sediment trap flux data to facilitate high resolution palaeoceanaographic and palaeoclimatic reconstructions throughout the holocene

the influence of shale depositional fabric on the kinetics of hydrocarbon generation through control of mineral surface contact area on clay catalysis abstract accurately assessing the temperature and hence the depth and timing of hydrocarbon generation is a critical step in the characterization of a petroleum system clay catalysis is a potentially significant modifier of hydrocarbon generation temperature but experimental studies of clay catalysis show inconsistent or contradictory results this study tests the hypothesis that source rock fabric itself is an influence on clay mineral catalysis as it controls the extent to which organic matter and clay minerals are physically associated two endmember clay organic fabrics distinguish the source rocks studied 1 a particulate fabric where organic matter is present as discrete 5 m particles and 2 a nanocomposite fabric in which amorphous organic matter is associated with clay mineral surfaces at sub micron scale high resolution electron imaging and bulk geochemical characterisation confirm that samples of the miocene monterey formation california are representative of the nanocomposite source rock endmember whereas samples from the permian stuart range formation south australia represent the particulate source rock endmember kinetic experiments are performed on paired whole rock and kerogen isolate samples from these two formations using open system non isothermal pyrolysis at three different heating rates 0 7 2 and 5 k min to determine the effects of the different shale fabrics on hydrocarbon generation kinetics extrapolation to a modelled geological heating rate shows a 20 c reduction in the onset temperature of hydrocarbon generation in monterey formation whole rock samples relative to paired kerogen isolates this result is consistent with the monterey formations s nanocomposite fabric where clay catalysis can proceed because reactive clay minerals are intimately associated with organic matter by contrast there is no significant difference in the modelled hydrocarbon generation temperature of paired whole rock and kerogen isolates from the stuart range formation this is consistent with its particulate fabric where relatively large discrete organic particles have limited contact with the mineral matrix and the clay minerals are mainly diagenetic and physically segregated within pores while heating rate may have a control on mineral matrix effects this result shows that the extent to which organic matter and clay minerals are physically associated could have a significant effect on the timing of hydrocarbon generation and is a function of the depositional environment and detrital vs diagenetic origin of clay minerals in source rocks

potential vorticity and layer thickness variations in the flow around jupiter s great red spot and white oval bc layer thickness variations in jupiter s atmosphere are investigated by treating potential vorticity as a conserved tracer starting with the horizontal velocity field measured from voyager images fluid trajectories around the great red spot grs and white oval bc are calculated the flow is assumed to be frictionless adiabatic hydrostatic and steady in the reference frame of the vortex absolute vorticity is followed along each trajectory its magnitude is assumed to vary directly as the thickness which is defined as the mass per unit area between potential temperature surfaces to the accuracy of the observations the inferred thickness is a separable function of trajectory and latitude the latitude dependence has positive curvature near the grs and bc the relative variations of thickness with respect to latitude are generally larger than the relative variations of coriolis parameter with respect to latitude the beta effect the data are a useful diagnostic which will help differentiate between models of jovian vortices the present analysis employs a quasi geostrophic model in which a thin upper weather layer which contains the vortex is supported hydrostatically by a much deeper lower layer in this model the upper free surface does not contribute to the observed variation of thickness along trajectories such variations are due exclusively to bottom topography flow of the deep lower layer relative to the vortex the observation are used to infer the form of the deep zonal velocity profile vs latitude the magnitude of the profile depends on the unknown static stability the principal result is the existence of horizontal shear in the deep layer zonal velocity profile i e the lower layer is not in solid body rotation and does not act like a flat solid surface in this respect the data support the hypothesis of ingersoll and cuong concerning motions in the deep layer however at some latitudes the data violate ingersoll and cuong s criterion governing the compactness of the vortices at these latitudes the topography allows standing rossby waves wakes extending far downstream to the west observed wavelike features the filamentary regions are possibly formed by this mechanism

moist convection as an energy source for the large scale motions in jupiter s atmosphere jupiter s dominant large scale weather patterns dimensions 10 000 km are zonal jets and long lived ovals the jets have been flowing east and west at constant speeds of up to 180 m s 1 for over 100 years these jets receive energy from small scale eddies which pump eastward momentum into the eastward jets and westward momentum into the westward jets this momentum transfer was predicted by numerical models before it was observed on jupiter the large ovals roll between the jets in an anticyclonic direction clockwise in the northern hemisphere and counterclockwise in the southern hemisphere where they regularly assimilate small anticyclonic eddies but from where the eddies receive their energy has been an open question here we argue that the eddies which ultimately drive both the jets and the ovals receive their energy from moist convection this hypothesis is consistent with observations of jovian lightning which is an indicator of moist convection it also explains the anticyclonic rotation and poleward drift of the eddies and suggests patterns of upwelling and downwelling that resemble the patterns of large scale axisymmetric overturning in the earth s atmosphere

the occurrence of isorenieratane and 24 n propylcholestanes in paleogene lacustrine source rocks from the dongying depression bohai bay basin implications for bacterial sulfate reduction photic zone euxinia and seawater incursions abstract lacustrine organic rich source rocks shales and mudstones were examined to assess the depositional environment and organic input sources of the third and fourth members of the eocene shahejie formation bohai bay basin china major organic contributions to the shahejie formation from dinoflagellates diatoms botryococcus and marine pelagophyte chrysophyte algae were determined using n alkane distributions gammacerane index and diagnostic steranes traces of higher plant biomarkers suggest that terrigenous organic inputs were limited the pervasive presence of carotane aryl isoprenoids paleorenieratane renieratane isorenieratane 2 methylhopanes and crocetane indicate significant organic contributions from bacterial communities including cyanobacteria purple sulfur bacteria chromatiaceae green sulfur bacteria chlorobiaceae and sulfate reducing bacteria the extent of h2s content bacterial sulfate reduction and photic zone euxinia pze were evaluated by determining the aryl isoprenoids ratio air 0 7 9 0 the presence of isorenieratene derivatives and the fate of sulfur in the water column there was a decrease of pze extent and duration from the northeast to the southwest of the palaeo lake and there was a decrease of water body salinity and bottom water anoxia from the fourth to the third member of the shahejie formation abrupt environmental perturbations in the third member of the shahejie formation are indicated not only by significant changes in parameters such as the pristane phytane and carotane n c20 alkane ratios the gammacerane index the isorenieratane c18 aryl isoprenoid and the air but also by the time lag in the expansion of cyanobacterial lineages after the expansion of purple green sulfur bacteria as well as seawater incursions the unexpected occurrence of intact c30 4 desmethylsteranes 24 n propylcholestanes in the shahejie formation is first reported here after very careful checking and provides unambiguous biological evidence for at least two marine transgression events reaching the eocene dongying palaeo lake the organic enrichment of the petroleum source rocks in the shahejie formation is a consequence of combined indigenous lacustrine algal production the constrained and favourable preservation conditions and significant bacterial contributions and marine organic matter inputs to the lake

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

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

jupiter s cloud structure from galileo imaging data the vertical structure of aerosols on jupiter is inferred from data obtained by the nasa galileo solid state imaging system during the first six orbits of the spacecraft images at 889 nm a strong methane band 727 nm a weaker methane band and 756 nm continuum taken at a variety of lighting and viewing angles are used the images are displayed and described in the companion paper by vasavada et al 1998 icarus 135 265 275 conservative scattering cloud particles with laterally uniform single scattering properties are assumed in the analysis and are shown to be consistent with the data at these wavelengths particles are bright and the darkest locations on jupiter correspond to the smallest optical thickness of aerosols optical depths and vertical positions of aerosol layers vary from place to place and are the retrieved quantities in the analysis only mid and low latitudes are sampled in this data set a stratospheric haze with an optical depth of roughly a tenth and an upper tropospheric haze with an optical depth of 2 to 6 exist over all regions both are consistent with previous conclusions based on data of lower spatial resolution e g west et al 1986 icarus 65 161 217 the new data show that these layers contain little lateral structure on scales smaller than the planetary jets on scales of the jets and ovals the top and bottom of the upper tropospheric haze vary in elevation the concentration of particles optical depth per pressure interval varies less than does the total optical depth near the base of the upper tropospheric haze is a third cloud component usually at pressure p 750 200 mb which is less than a scale height in geometric thickness its optical depth varies from zero to about 20 on regional scales and often varies by 50 on scales of a few tens of kilometers optical depth variations in this cloud are the principal cause of the features in jupiter s atmosphere seen at red and longer wavelengths it is probably composed of ammonia the expected nh 4sh cloud has not been identified in this work perhaps because it exists only at locations where it is concealed beneath higher clouds our retrievals also cannot rule out a pervasive deep haze without small scale structure finally in one region northwest of the great red spot a deeper cloud is identified parts of it lie at a pressure greater than four bars it is associated with a rapidly changing storm system with optical depth of several tens or more and a range of cloud heights between p 4 bars to p 400 mb it is probably composed of water

a comparison of thermal maturity parameters between freely extracted hydrocarbons bitumen i and a second extract bitumen ii from within the kerogen matrix of permian and triassic sedimentary rocks abstract in this study we compared various maturity dependent aromatic steroid and triterpenoid hydrocarbon ratios in bitumens that are freely extractable from sedimentary rocks bitumen i with those in second extracts that comprised hydrocarbons closely associated with the kerogen mineral matrix bitumen ii bitumen ii was released through kerogen isolation and demineralisation using hcl and hf h3bo3 the samples studied although of similar age come from different localities they represent a range of facies and two kerogen types ii and iii and all were deposited under marine conditions the results show that the more stable isomers of methylnaphthalene mn and methylphenanthrene mp are relatively more abundant in bitumen ii the difference between the methylnaphthalene ratio mnr of bitumens i and ii when plotted against the ratio of clay to total organic carbon clay toc gives an excellent correlation r2 0 88 the highest clay toc ratio corresponds with the biggest difference in mnr for the respective bitumens consistent with the more stable isomers being preferentially retained within the clay kerogen matrix since the mp isomers are higher in bitumen ii than in bitumen i it was anticipated that their methylphenanthrene index mpi 1 values a commonly used measure of thermal maturity would also be different for most samples the measured mpi 1 in bitumen i is generally higher than that in bitumen ii except for three samples thus showing a bias towards a lower thermal maturity for the second extract the opposite is true of the mp ratio and mnr this may be attributed to the fact that phenanthrene p which is part of the denominator in mpi 1 is more stable than its methylated counterparts steroid and triterpenoid maturity parameters also showed differences between the two extracts with c27 diasterane sterane and ts ts tm being higher in bitumen i only the former parameter is positively correlated with the clay toc ratio suggesting that clay content probably influences the diagenetic transformation of steroid precursors to diasteranes the observed differences between the maturity parameters of bitumen i and bitumen ii may be especially important in sedimentary rocks that contain high percentages of clay minerals

dynamics of saturn s great storm of 2010 2011 from cassini iss and rpws saturn s quasi periodic planet encircling storms are the largest convecting cumulus outbursts in the solar system the last eruption was in 1990 sanchez lavega a 1994 chaos 4 341 353 a new eruption started in december 2010 and presented the first ever opportunity to observe such episodic storms from a spacecraft in orbit around saturn fischer g et al 2011 nature 475 75 77 sanchez lavega a et al 2011 nature 475 71 74 fletcher l n et al 2011 science 332 1413 here we analyze images acquired with the cassini imaging science subsystem iss which captured the storm s birth evolution and demise in studying the end of the convective activity we also analyze the saturn electrostatic discharge sed signals detected by the radio and plasma wave science rpws instrument the storm s initial position coincided with that of a previously known feature called the string of pearls sops at 33 n planetocentric latitude intense cumulus convection at the westernmost point of the storm formed a particularly bright head that drifted at 26 9 0 8 m s 1 negative denotes westward motion on january 11 2011 the size of the head was 9200 km and up to 34 000 km in the north south and east west dimensions respectively rpws measurements show that the longitudinal extent of the lightning source expanded with the storm s growth the storm spawned the largest tropospheric vortex ever seen on saturn on january 11 2011 the anticyclone was sized 11 000 km by 12 000 km in the north south and east west directions respectively between january and september 2011 the vortex drifted at an average speed of 8 4 m s 1 we detect anticyclonic circulation in the new vortex the vortex s size gradually decreased after its formation and its central latitude shifted to the north the storm s head moved westward and encountered the new anticyclone from the east in june 2011 after the head vortex collision the rpws instrument detected that the sed activities became intermittent and declined over 40 days until the signals became undetectable in early august in late august the sed radio signals resurged for 9 days the storm left a vast dark area between 32 n and 38 n latitudes surrounded by a highly disturbed region that resembles the mid latitudes of jupiter using iss images we also made cloud tracking wind measurements that reveal differences in the cloud level zonal wind profiles before and after the storm

early diagenetic pyrite cementation influences molecular composition of sedimentary organic matter in the dongying depression china abstract micro variations of lipid hydrocarbons and biomarkers in well laminated shales have not been extensively documented especially within different rock textures fabrics and mineralogies comparison of a pyrite cemented zone and its surrounding sediment may offer a new perspective on mineral control on preservation of hydrocarbons and organic carbon a black well laminated shale comprising two adjacent and contrasting calcareous light and pyrite dark laminae at the millimetre scale was selected from the eocene shahejie formation dongying depression bohai bay basin it was horizontally sliced to separate a pyrite cemented concretion from the unaltered laminated shale and investigated using geochemical techniques to assess the heterogeneity of elements minerals microfossils and hydrocarbons within the two slices micro scale changes in source inputs were noted for instance the 4 methylsteranes dinosteranes and the triaromatic dinosteranes show varying distributions between the two slices attributed to slight differences in dinoflagellate contributions similarly variation in the amount of bacterial sulfate reduction is indicated by variations in the aryl isoprenoid ratio relative amount of isorenieratane long chain n alkane carbon isotopic composition and other molecular indicators including the relative amounts of dibenzothiophene dibenzofuran methyldibenzothiophene and methyltrimethyltridecylchromans the primary control on these variations appears to be different euxinic water conditions but diagenesis has also influenced the distributions differential anaerobic bacterial reworking of organic matter and pyrite concretion protection are responsible for organic geochemical variations on a millimetre scale in the shale the pyrite concretion has an altered record of its thermal history but has a more accurate record of the organic geochemistry of microfossils and water column conditions this study shows the potential for future investigations of closely spaced vertical variation in organic geochemical parameters that may shed light on rapid temporal variation in organic matter input and depositional environment

effect of maturity on 13c12c ratios of individual compounds in north sea oils abstract carbon isotope variations in individual compounds are reported for north sea oils of variable thermal maturity using the pristane phytane ratio of the oils as an indication of source facies variation and molecular maturity ratios to determine maturity it is possible to differentiate the two effects in these samples maturity accounts for between 50 and 90 of the observed isotopic variation all values becoming heavier with increasing maturity typically by between 2 and 3 however source differences are also apparent with a terrestrially influenced source possibly the heather formation contributing material to the kimmeridge clay sourced oils the heather contribution is isotopically heavier than the kimmeridge oil for most compounds but is isotopically lighter for the isoprenoid hydrocarbons and some other branched compounds it is also more important for lower molecular weight hydrocarbons than for higher homologues

polar lightning and decadal scale cloud variability on jupiter although lightning has been seen on other planets including jupiter polar lightning has been known only on earth optical observations from the new horizons spacecraft have identified lightning at high latitudes above jupiter up to 80 n and 74 s lightning rates and optical powers were similar at each pole and the mean optical flux is comparable to that at nonpolar latitudes which is consistent with the notion that internal heat is the main driver of convection both near infrared and ground based 5 micrometer thermal imagery reveal that cloud cover has thinned substantially since the 2000 cassini flyby particularly in the turbulent wake of the great red spot and in the southern half of the equatorial region demonstrating that vertical dynamical processes are time varying on seasonal scales at mid and low latitudes on jupiter

chemostratigraphy of the posidonia black shale sw germany ii assessment of extent and persistence of photic zone anoxia using aryl isoprenoid distributions aquatic depositional environments where anoxic conditions extend from bottom waters into the photic zone occurred frequently during the geologic past periods of photic zone anoxia pza can be recognized by the presence of specific lipids produced exclusively by the green sulphur bacteria chlorobiaceae that are preserved in the sedimentary record chlorobiaceae perform anoxygenic photosynthesis that requires light penetration into h2s saturated waters sediment samples integrate paleoenvironmental conditions over time intervals ranging from at best a few decades to more commonly several millennia photic zone anoxia recognized in paleoenvironmental analyses is thus defined as episodic with no further interpretation on the duration and persistence of the anoxic events we provide here a high resolution multiproxy chemostratigraphy study for the toarcian posidonia black shale from the dotternhausen section in sw germany in order to assess duration and seasonal fluctuation of photic zone anoxia based on the relative abundance of derivatives of chlorobiaceae lipids we assess the variability in the degree and persistence of photic zone anoxia using an aryl isoprenoid ratio air obtained by calculating the proportion of the short chain c13 17 versus the intermediate chain c18 22 aryl isoprenoids higher relative abundance of the short chain analogues is interpreted as indicating more intensive aerobic degradation of aryl isoprenoids air varies between values of 0 5 indicative of persistent pza phases and 3 0 for short termed episodic pza events absolute concentration of aryl isoprenoids is negatively correlated with the air which is in agreement with a progressive diagenetic breakdown of aryl isoprenoids the air decreases are validated using independent palecological and geochemical redox indicators for the posidonia shale in sw germany d 2004 elsevier b v all rights reserved

molecular isotopic characterisation of hydrocarbon biomarkers in palaeocene eocene evaporitic lacustrine source rocks from the jianghan basin china immature organic matter in lacustrine source rocks from the jianghan basin eastern china was studied for distributions and stable carbon isotopic compositions 13 c of hydrocarbon biomarkers all of the bitumens contain isorenieratane 13 c ca 17 indicating the presence of chlorobiaceae and thus periods of euxinic conditions extended into the photic zone aliphatic hydrocarbon fractions are dominated by pristane and phytane and contain relatively low amounts of 4a and 4 methylsteranes c 30 13 c ca 16 believed to originate from 4 methylsterols in dinoflagellates 13 c values of gammacerane ca 24 and c 30 17 21 h hopane ca 23 are consistent with an origin from bacterivorous ciliates that fed on chlorobiaceae the bitumens contain low relative amounts of organo sulphur compounds one rock contains c 37 and c 38 n alkanes 13 c ca 36 derived from alkadienes and alkenones of prymnesiophytes the distributions of hydrocarbon biomarkers suggest that they were initially sulphurised during early diagenesis and later released during early thermal maturation

molecular stable carbon isotope compositions of alkylphenanthrenes in coals and marine shales related to source and maturity abstract phenanthrene phe and methylphenanthrenes mps extracted from coaly shale and coal samples containing terrestrial organic matter are compared with the same compounds from marine shales in terms of yields and 13 c values at marginally to fully mature stages of thermal evolution the shales derived from four boreholes in the hils half graben area northwestern germany were shown to be representative of a greater number of samples from the same sites the 13 c values of extractable phe and mps are less negative in the terrestrial 24 3 to 26 0 than in the marine 28 8 to 30 5 samples since these values are unrelated to mean vitrinite reflectance r r values in the range of 0 5 0 9 it appears that the stable carbon isotope composition of phe and mps is controlled by organic matter type rather than maturity

microbially mediated fossil bearing carbonate concretions and their significance for palaeoenvironmental reconstructions a multi proxy organic and inorganic geochemical appraisal carbonate concretions are widespread within the geological record however the lack of recent known analogues creates a need for novel approaches to unravel the major microbial players involved in concretion formation and establish their suitability as palaeoenvironmental recorders here we used a combination of geochemical and geological techniques to study two pyritiferous calcite concretions and compared the results with their host sediment toarcian posidonia shale 183 ma sw germany the c 13 depleted nature of the concretion bodies with average values of delta c 13 carb 14 8 delta c 13 org 32 4 and delta c 13 n alkanes 34 9 indicates that sulphate reducing bacteria srb played a major role in the concretion growth and preservation of the nucleus via the rapid decomposition of organic matter om however rock eval analyses from both concretions revealed elevated hydrogen indices hi in the body and low hi values at the rim these values suggest that most of the microbial activity did not occur in the concretion body but rather at the rim and at the surface of the nuclei which generally supports the exceptional preservation of om in carbonate concretions furthermore enrichment in euhedral pyrite in the concretion rims suggests they were formed through increased activities of iron reducing fer bacteria coupled to a decrease of srb activity leading towards conditions more favourable to the direct precipitation of pyrite despite low delta c 13 values the known lipid biomarkers such as acyclic extended isoprenoids or 3 beta methyl hopanes did not reveal evidence of an active methane cycling the present study emphasises the crucial role of carbonate concretion in om preservation and highlights their great potential as palaeoenvironmental recorders c 2016 elsevier b v all rights reserved

mudstones and embedded concretions show differences in lithology related but not source related biomarker distributions abstract the mudstones of the western australian gogo formation harbour numerous carbonate concretions which often contain preserved fossils of lagerstatte like quality these are especially notable in places where the mudstone has eroded giving way to nodule fields which afford valuable paleobiological records it is however a challenge to determine their paleoenvironmental context here we analysed concretions from a core drilled in the canning basin gogo formation at two different depths concretions were compared to the surrounding mudstone found at the same depth electron microscopy and x ray spectroscopy showed that the concretions were carbonate rich and contained detrital fragments biomarker data showed that mudstone and concretions had very similar distributions and presented marine biosignatures including indicators of anoxic depositional conditions a stratified water column and photic zone euxinia the concretions contained higher amounts of c 27 steranes indicating that more labile organic matter such as animal remains could have triggered concretion formation statistical analyses of the results showed that concretions and shales differed p p 31 homohopanes and hopane sterane ratios p

intermediate and deep seismicity and lateral structure of subducted lithosphere in the circum pacific region in this paper we present a region by region review of the wadati benioff zone structure of most of the world s seismically active subduction zones focusing primarily on the intermediate and deep seismicity lateral changes in wadati benioff zone structure are common in every major subduction zone in this study we use these changes to define possible boundaries between portions or segments of lithosphere with differing subduction geometries although earthquake data seldom have the resolution to show conclusively whether these boundaries separate independent blocks of lithosphere the available data indicate that the active process at most of these segment boundaries is ductile deformation of the subducting plate rather than tearing we found the strongest evidence for the existence of tears where tears are geometrically necessary such as where a transform boundary terminates a trench as at the new hebrides tonga and south sandwich trenches weak evidence suggesting other tears does exist in some regions such as taiwan the japan izu bonin corner and the philippines the causes of these changes in structure are in most cases unclear only about 34 of the possible segment boundaries coincide with subducting bathymetric features some boundaries occur where there is apparent lateral strain caused by anomalous trench geometry we have designed a simple modeling procedure which incorporates published plate motion and the observed geometry of trenches and wadati benioff zones to estimate the lateral strain in subduction zones throughout the circum pacific region although no observed subduction zone has a perfectly strain free geometry there is a broad range of geometries for which the lateral strain is small indeed the observed geometry of most subduction zones involve relatively little lateral strain comparison with centroid moment tensor focal mechanisms indicates that in zones where the modeling predicted little lateral strain the mechanisms of intermediate and deep earthquakes show no effects of lateral stress and downdip stresses are clearly dominant in regions such as the mariana arc where the model predicts very large lateral extension lateral tension is very evident in the focal mechanisms in regions such as the hokkaido corner where the modeling predicts large compressional strains the plate appears to buckle and bending stresses parallel to the trench are evident in general this study finds that subducted lithosphere is remarkably cohesive and rigid and only rarely deforms by breaking or stretching

biomarker evidence for two sources for solid bitumens in the subu wells implications for the petroleum prospectivity of the east papuan basin abstract late cretaceous sandstones from the subu 1 and 2 wells aure scarp papua new guinea contain patchily distributed solid bitumens the solid bitumens vary in reflectance and geochemistry indicating that they formed by the biodegradation of two different families of crude oils termed family a and family b biomarker characteristics such as the high abundance of rearranged hopanes and steranes indicate that the family a solid bitumens were derived originally from a clay rich marine source rock low in sulphur which had significant input of terrestrial organic matter these correlate with oils from the iagifu 7x gobe 3x omati 1 and puri 1 wells that are believed to be generated from sources of jurassic age the family b solid bitumens and a fluid inclusion oil from subu 1 have a high abundance of 2 methylhopanes bisnorhopanes and dibenzothiophene and originated from a marine source rock with a calcareous component this source rock had a high proportion of prokaryotic organic matter input a greater sulphur content and a more reducing depositional environment than the jurassic source rocks the lack of correlation with other oils in papua new guinea suggests the presence of a second so far unidentified generative marine source rock in the east papuan basin the fine grained samples in the subu wells are thermally immature vre 0 5 0 6 organically lean and contain type iii organic matter with little hydrocarbon generation potential most of the solid bitumens have peak oil window thermal maturities vre 0 8 1 0 but some have lowered maturities that are interpreted to be due to co extraction of indigenous detrital low maturity organic matter low molecular weight n alkanes alkylcyclohexanes methylalkylcyclohexanes and alkylbenzenes in many of the samples are attributed to overprinting of pre existing variably biodegraded solid bitumens in the sandstones with pristine hydrocarbon charge with a condensate composition this condensate charge has not undergone any major biodegradation or water washing implying that it is a relatively recent event solid bitumen from a vein in a miocene volcanolithic sandstone from the ouha anticline was generated from an early mature palaeogene or late cretaceous source rock that contained predominantly terrestrial organic matter deposited in an oxic environment this sample proves the existence of a different oil generative source rock in the east papuan basin in addition to the two oil source rocks inferred from the subu data

source and significance of selected polycyclic aromatic hydrocarbons in sediments hovea 3 well perth basin western australia spanning the permian triassic boundary abstract stable carbon isotopic data for polycyclic aromatic hydrocarbons pahs chrysene and triphenylene benzo e pyrene 9 methylphenanthrene in sediments of comparable thermal maturity from a petroleum drill core hovea 3 well perth basin western australia spanning the largest mass extinction event in the past 500 million years permian triassic boundary are consistent with an algal kerogen source in the basal triassic as opposed to a combustion and or higher plant source in the underlying permian sediments the 13c values of extractable pahs are less negative in the permian inertinitic interval 24 7 to 29 2 than the triassic sapropelic interval 30 to 33 3 a strong correlation is evident between 13c of individual pahs 13c of kerogen and rock eval pyrolysis hydrogen index providing unequivocal evidence that pah 13c is mainly controlled by organic matter type abundant algal derived pahs in basal triassic sediments may be a global feature the lack of coal globally in the basal triassic sediments is also consistent with this observation the early triassic coal gap appears to coincide with the global extinction of peat forming plants at the end of the permian coal did not reappear until the middle triassic and permian levels of plant diversity and thick peat deposits did not recover until the late triassic the pah isotopic data support the contention that a global anoxic event at the end of the permian period contributed to the gradual worldwide asphyxiation and ultimate extinction of many marine and terrigenous organisms

controls of subduction geometry location of magmatic arcs and tectonics of arc and back arc regions most variation in geometry and angle of inclination of subducted oceanic lithosphere is caused by four interdependent factors combinations of 1 rapid absolute upper plate motion toward the trench and active overriding of the subducted plate 2 rapid relative plate convergence and 3 subduction of intraplate island seamount chains aseismic ridges and oceanic plateaus anomalously low density oceanic lithosphere cause low angle subduction under conditions of low angle subduction the upper surface of the subducted plate is in contact with the base of the overlying plate the wedge of low density asthenosphere is replaced by subducted lithosphere and the width of the arc trench gap either is significantly increased or a magmatic arc is not developed within the overlying plate the fourth factor is age of the subducting lithosphere subduction of young lithosphere produces two opposing tendencies 1 low angle subduction and increased arc trench distance owing to its low density and 2 decreased arc trench distance owing to its higher temperature two factors of secondary importance contribute to variation in subduction zone geometry and arc trench distance accretion of sediment in trenches depresses the upper portion of the subducting oceanic plate and causes the trench axis to migrate seaward prolonged subduction thickens the upper plate depresses the isotherms in the subducted plate and may create a broader arc both factors increase the arc trench gap the four primary factors also control development of other tectonic elements such as regional subsidence for example the amazon basin and a portion of the cretaceous interior seaway of western united states intra arc extension for example the basin and range province foreland fold and thrust belts and laramide style tectonics

reconstructing the palaeoecosystem and palaeodepositional environment within the upper devonian lower mississippian bakken formation a biomarker approach abstract biomarkers have been used extensively to correlate oil families oil source rock relationships and source inputs and to help identify the palaeodepositional environment for a given geological sedimentary unit despite their application in characterising the bakken formation shales a number of biomarkers still appear unable to provide us a consistent understanding regarding heterogeneity in source organic matter and palaeoenvironment here we infer the palaeodepositional environment within the bakken formation shales using a biomarker suite and biomarker depth profiles we also use the occurrence and abundance of biomarkers to define organic facies and to make inferences regarding biotic interactions drawn from modern analogues the variations and co occurrence of biomarkers is explained by the existence of a proposed complex algal bacterium bacteriovore palaeoecosystem this approach not only helps explain the depth variation in occurrence and concentration of biomarkers and the molecular composition of associated organic matter but also advances the use of biomarker analysis and biomarker associations to determine a complex environment sensitive palaeoecosystem

prediction of a global climate change on jupiter jupiter s atmosphere as observed in the 1979 voyager space craft images is characterized by 12 zonal jet streams and about 80 vortices the largest of which are the great red spot and three white ovals that had formed1 in the 1930s the great red spot has been observed2 continuously since 1665 and given the dynamical similarities between the great red spot and the white ovals the disappearance3 4 of two white ovals in 1997 2000 was unexpected their longevity and sudden demise has been explained5 however by the trapping of anticyclonic vortices in the troughs of rossby waves forcing them to merge here i propose that the disappearance of the white ovals was not an isolated event but part of a recurring climate cycle which will cause most of jupiter s vortices to disappear within the next decade in my numerical simulations the loss of the vortices results in a global temperature change of about 10 k which destabilizes the atmosphere and thereby leads to the formation of new vortices after formation the large vortices are eroded by turbulence over a time of 60 years consistent with observations of the white ovals until they disappear and the cycle begins again

the distribution of molecular fossils derived from dinoflagellates in paleogene lacustrine sediments bohai bay basin china steroids with unconventional side chains in ancient sediments and petroleum have been increasingly used as age diagnostic markers triaromatic dinosteroids and dinosteranes occur widely throughout the eocene oligocene shahejie formation in the southeastern bohai bay basin china consistent with its abundant fossil dinoflagellate assemblages in addition 24 norcholestane biomarkers which commonly appear in marine oils have been found in this lacustrine formation although a firm link has not been established between 24 norcholestane and specific modern taxa both diatoms and dinoflagellates are shown to be likely sources of 24 norcholestanes although the shahejie strata lack intact diatom frustules they do exhibit a good relationship between 24 norcholestane other molecular fossils of dinoflagellates and dinocysts dinoflagellates are important precursor taxa of 24 norcholestanes and the various species identified in eocene oligocene lacustrine shales and mudstones of the shahejie formation are all potential sources of the 24 norcholestanes

molecular proxies as indicators of freshwater incursion driven salinity stratification salinity related stratification in marine environments is one of the main drivers for the development of persistent anoxia and euxinia it therefore plays a vital role in the sedimentary preservation of organic matter and has also been associated with oceanic anoxic events during several mass extinctions in earth s history here we present a novel molecular proxy using relative abundances of methyltrimethyltridecylchromans mttcs as indicators of riverine freshwater incursions into middle to late devonian paleoreefs exposed to conditions of prevailing anoxia photic zone euxinia and water column stratification this paper aims at re instigating a discussion about the origin of these compounds to potentially broaden their utilization as paleoproxies adding freshwater stratification to the general salinity reconstructions the co variation of mttc abundance profiles and 13c values with other biomarker parameters in the sediments studied here indicate a link of mttcs to terrigenous input pointing towards a previously suggested early diagenetic formation of these compounds from phytol with higher plant derived alkylphenols

aliphatic and aromatic biomarkers from gondwanan sediments of late ordovician to early devonian age an early terrestrialization approach abstract twenty one core samples of late ordovician to early devonian age from sections in southern tunisia north african platform gondwana and containing marine and terrestrial organic matter with microbial input were investigated to link the aliphatic and aromatic hydrocarbon distributions with the terrestrial and marine palynomorph content e g acritarchs prasinophytes chitinozoans cryptospores and trilete spores in addition to several biomarkers of algal bacterial origin long chain n alkanes that might be derived from land plants as well as the terrestrial diterpane norabietane were found several land plant derived biomarkers such as retene cadalene simonellite tetrahydroretene and c19 isohexylalkyl naphthalene were observed in the aromatic fractions while these terrestrial biomarkers could be clearly recognized in the middle silurian lower devonian samples their presence in the upper ordovician lower silurian sediments is more doubtful because of much lower relative abundances the land plant biomarkers show a fairly good correlation with the occurrence and abundance of cryptospores and trilete spores derived from bryophytes and tracheophytes which covered the emerged areas around the ghadamis basin during the silurian and devonian the early tracheophytes e g cooksonia lycophytes and zosterophylls are therefore suggested as a new terrestrial source for most of the saturated and aromatic biomarkers found in sediments of middle silurian to early devonian age

variation in stable carbon isotope ratios of individual hydrocarbons as a function of artificial maturity abstract this paper reports isotopic variations in n alkanes isoprenoids and terpenoids from different source rock types as a function of maturity by analysis of these compounds in hydrous pyrolysis products and oil at high pyrolysis temperatures n alkanes isoprenoids and terpenoids in the pyrolysis products become depleted in 12 c the most marked depletion occurs in the terpenoids particularly in the c 29 c 31 hopanes these compounds are isopically very light in the immature unheated samples of the lacustrine green river shale tertiary and a guatemalan carbonate source rock there is a marked depletion in 12 c at 330 c and higher pyrolysis temperatures for these two samples moderately mature samples of the toarcian paris basin shale and a jurassic coal from the hammerfest basin showed less or no 12 c depletion fairly uniform values were recorded for the hopanes in pyrolysates of all samples heated at temperatures of 350 c and above the isotopic composition of n alkanes and isoprenoids are fairly similar to the hopanes in samples pyrolysed at the higher temperatures it appears therefore that with increasing maturity n alkanes isoprenoids and terpenoids become fairly similar in their carbon isotopic composition the isotopic compositions within the different compound groups in the different source rocks are sufficiently different for this technique to be used in source rock oil correlation

the 1977 sumba earthquake series evidence for slab pull force acting at a subduction zone the great 1977 sumba earthquake occurred at the eastern sunda trench just west of the collision of australian continental lithosphere with the island arc the length of the aftershock zone of this normal faulting earthquake is about 200 km aftershocks are concentrated 65 115 km east of the main shock epicenter with very few aftershocks in a 50 km long segment that spans the main shock epicenter relocated hypocenters and focal mechanism data are consistent with normal faulting throughout the upper 28 km of the oceanic lithosphere there is no evidence for thrust faulting of the deeper aftershocks these data imply that the neutral bending surface must be at least 35 40 km deep a second aftershock zone about 180 km northwest of the main shock became active immediately following the main shock but events were concentrated during days 50 52 this zone is a 70 km long lineation that trends toward the main shock epicenter and reflects right lateral strike slip faulting within the subducted oceanic plate seismicity exists to a depth of about 650 km in the very old plate beneath the sunda banda arc and that plate s negative buoyancy causes very large slab pull forces great interface thrust earthquakes are absent at the sumba region and slab pull forces are inferred to have partially decoupled the subducted plate from the overriding plate this decoupling permits slab pull stresses to be guided updip to the region of the sumba main shock such shallow acting slab pull provides a bending moment at the trench and explains the deformation and timing observed for the entire sumba earthquake series in this model slab pull forces stretch the subducted plate until the increasing stresses at the shallow subduction zone lead to a subduction zone earthquake postseismically the released oceanic plate undergoes a pulse of downdip strain returning the plate to a less extended state the moment of this downdip plate motion could exceed the seismic moment of the main shock

evidence for photic zone euxinia in the early albian santana formation araripe basin ne brazil organic matter from two black shale units in the santana formation araripe basin ne brazil has been studied to investigate the palaeoenvironmental conditions prevailing during formation of this famous fossil lagerstatte optical and organic geochemical analyses indicate a predominantly autochthonous source with very limited terrestrial input molecular fossils of green sulphur bacteria show that the water column was stratified with euxinic conditions reaching up into the photic zone thus mass mortality events of fish may be explained by intrusion of sulphide containing waters the low quantity of material derived from land plants in this interior marine setting is interpreted to reflect a consequence of enhanced marine productivity resulting in dilution of the continental signal different depositional scenarios are proposed to explain our findings including 1 coastal erosion and nutrient leaching during a transgressive event 2 intrusion of euxinic waters during an early albian oae or 3 an estuarine circulation pattern associated with thermohaline stratification

focal depths and moment tensor representations of shallow earthquakes associated with the great sumba earthquake focal depths in the range 8 to 24 km below the seafloor were determined for seven of the larger shocks associated with the great sumba earthquake of august 19 1977 depth control was achieved by modeling digitized long period p waves recorded by the world wide standard seismic network if the base of the rupture at the time of the mainshock were no greater than the depth of the deepest aftershock the stress drop would be nearly 500 bars amplitude and first motion data from the p waves were inverted for point source moment tensors the inversion of rayleigh and love wave spectra computed from digital seismograms recorded by the seismic research observatories sro and the abbreviated seismic research observatories asro broadened the source study to include earthquakes with moments as small as 1024 dyn cm too small for either traditional first motion solutions or p wave modeling the inversion procedure was applied to data in the passband from 30 to 120 s the propagation phase for the love and the rayleigh waves was calibrated with signals from two earthquakes for which the source phase was inferred from the p wave solutions agreement with the corresponding p wave solutions is nearly the same whether or not the smaller eigenvalues of the inner product matrix are retained in the inversions the double couple components generally account for more than two thirds of the total moment normal faulting along an east to northeasterly strike characterizes the mechanisms in the principal zone of aftershock activity strike slip mechanisms consistent with horizontal compression normal to the arc prevail in the delayed aftershock zone located 200 km northwest of the mainshock of the earthquakes subjected to this surface wave analysis the foreshock stood out as having felt a significantly higher apparent stress perhaps as much as one half an order of magnitude higher than the others these results suggest that accurate source parameters for moderate to small magnitude earthquakes can be determined from surface waves recorded by the sro and asro in particular the mechanisms of small magnitude foreshocks could be obtained in this way

paleosalinity significance of occurrence and distribution of methyltrimethyltridecyl chromans in the upper cretaceous nenjiang formation songliao basin china abstract a group of methyltrimethyltridecyl chromans mttcs was found in core samples of member 1 k 2 n 1 and member 2 k 2 n 2 of the nenjiang formation upper cretaceous from the sk l southern borehole songliao basin china they are assigned for the first time in sediments older than the tertiary in china their composition and distribution are indicative mainly of the redox and salinity conditions in the depositional environment the mttc isomer is in relatively higher abundance in samples from enhanced salinity and reducing conditions but was not detected in samples from aerobic and low salinity environments while mttc appears to be present in samples from environments with a broad range of salinity and redox conditions the mttc mttc ratio has a similar indication as that of the ratio and could be used as a corroborative ratio of paleosalinity a combination of biomarker parameters suggests that the massive lacustrine petroleum prone source rocks associated with the k 2 n 1 interval were likely developed under a stratified water column with enhanced salinity and an anoxic bottom water layer associated with a much less saline fresh to brackish upper water layer

distributions and stable carbon isotopic compositions of biomarkers in torbanites from different palaeogeographical locations abstract the relative distributions and stable carbon isotopic compositions of certain aliphatic and aromatic biomarkers from 11 botryococcus braunii rich torbanites from scotland south africa and australia covering the late carboniferous to late permian were investigated the data was scrutinised for any evidence of molecular features which may be characteristic of palaeogeography the torbanites studied were selected to cover a range of age and palaeoclimatic conditions e g permian and late carboniferous when gondwana was covered by an extensive ice sheet the late permian when the climate warmed from glacial to cool to temperate and the carboniferous when laurasia was located within the equatorial zone all torbanites are composed of abundant n alkanes and novel macrocyclic alkanes which based on similar 13c values are ascribed a common origin all samples are also characterised by a high cyanobacterial input as indicated by abundant hopanoids other biomarker distributions and stable carbon isotopic compositional differences separated the torbanites into three groups which also correlate to three different palaeogeographical palaeoclimatic precincts i group a southern africa and eastern australia temi torbanites which are characterised by a high relative abundance of cyanobacterial and methylotrophic hopanoids abundant branched hydrocarbons and 13c enriched homologous series of monomethylakanes ii group b eastern australia newnes and glen davis torbanites contain relatively high amounts of drimanes and abundant 13c enriched homologous series of monomethylakanes and iii group c scottish torbanites torbane hill and westfield contain high relative amounts of cyanobacterial hopanoids methylotrophic hopanoids and abundant branched aliphatics but no 13c enriched homologous series of monomethylakanes

total moment spectra of fourteen large earthquakes total moment spectra mt m where m is the moment rate tensor are computed for 14 large earthquakes recorded by the international deployment of accelerometers ida network using the scalar moment retrieval method proposed by silver and jordan 1982 for each event we obtain estimates of mt averaged over the 10 disjunct 1 mhz intervals in the low frequency band 1 11 mhz typical ida record sets from events with mt 0 2 a 1 a 1027 dyne cm yield standard errors on the 1 mhz averages that are generally less than 20 our multiple band estimates of mt are usually consistent with comparable single band values found by other investigators from the total moment spectra we derive the zero frequency static moment mt 0 and the characteristic source duration c 2 var f t where f t is the time function of the moment rate tensor assumed to be the same for all components the parameter c formally depends on the second degree temporal spatial and mixed spatial temporal moments of an extended source but calculations with realistic source geometries indicate that the interpretation of tc strictly in terms of the second temporal moment leads to very little error a plot of c against shows considerable scatter some events lie significantly above the empirical scaling curve of kanamori and given 1981 slow earthquakes and some below fast earthquakes examples of the former include all three deep focus events analyzed here as well as the 1970 colombia and 1963 peru bolivia deep focus earthquakes whose total moment spectra are calculated from the moment tensor solutions of gilbert and dziewonski 1975 an example of the latter is the great sumbawa earthquake of august 9 1977 24 3 a which is inferred to have a relatively shallow spatial centroid 20 km and a nearly flat moment spectrum suggesting that the faulting was confined to the upper more brittle portion of the oceanic lithosphere three other large earthquakes tonga june 22 1977 23 2 a kuril islands december 6 1978 3 6 0 2 a and tumaco december 12 1979 25 2 a exhibit moment spectra which significantly decrease toward higher frequencies indicating larger values of c the aftershocks of both the tonga and kuril islands events are distributed over a considerable range of depths consistent with rupture into the lower more ductile portions of the oceanic lithosphere we speculate that the characteristic source duration may be causally related to the depth of coseismic rupturing within the lithosphere

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