paleomagnetism of the permian triassic intrusions from the tunguska syncline and the angara taseeva depression siberian traps large igneous province evidence of contrasting styles of magmatism abstract based on the detailed paleomagnetic investigation we distinguished different styles of intrusive magmatic activity in two regions of the siberian traps large igneous province lip the emplacement of intrusions in the angara taseeva depression the southern periphery of the siberian traps lip occurred as brief but intense bursts of magmatic activity that led to the emplacement of large and extensive sills we argue that this pulsating style of intrusive magmatic activity is common for the margins of the siberian traps lip we also estimated the duration of the main magmatic events as 200 250 km in diameter and dozens of thousands km2 in square on the contrary in the central part of the siberian traps lip the tunguska syncline the intrusive magmatism was more or less continuous without intense peaks of magmatic activity furthermore we obtained the first reliable magnetostratigraphic data from the volcanic section of the tunguska syncline finally we analyzed the available paleomagnetic and geochronological data from the siberian platform and suggested the correlation scheme of the studied intrusive complexes with the volcanic sequences of the siberian traps lip

large scale traveling ionospheric disturbances observed by gps total electron content during the magnetic storm of 29 30 october 2003 1 we have investigated the propagation of large scale traveling ionospheric disturbances lstids during the super magnetic storm of 29 30 october 2003 two dimensional total electron content tec perturbation maps over north america were built using tec data provided by the american gps network and the international gnss service three lstid events were observed in the range of 30 degrees n 50 degrees n 60 degrees w 110 degrees w during this period the first two lstids occurred consecutively during 0620 0800 ut on 29 october at the local time of midnight right after the onset of the big substorm the third one was found at noon during the expansion phase of another substorm on 30 october the phase fronts of these lstids passed over the united states and traveled southwestward to the distance of similar to 2000 km with the maximum front width of similar to 4000 km and the duration of less than 2 hours the maximum amplitude of tec perturbations attained 3 total electron content units tecus the results differ from the former observation of afraimovich and voeykov 2004 and afraimovich et al 2006 who reported a solitary lstid propagating southwestward over the united states with the amplitudes of up to 14 tecu on 30 october 2003 we have checked the magnetic h component observed at the geomagnetic observatories in north america and found it is most likely that the auroral westward electrojet was the cause of the lstids on 29 october the source region for these tids was likely to be located several hundred kilometers north of 50 degrees n cross spectral analysis was conducted to obtain the global propagation characteristics of lstids during this superstorm equatorward lstids were found in all the three sectors of north america europe and asia showing high correlation with the occurrence of auroral substorms

a deforming plate tectonic model of the south china block since the jurassic abstract the south china block has experienced multiple phases of tectonic deformation since the middle jurassic understanding this deformation history helps reveal the driving mechanisms responsible and sheds light on the associated magmatism and mineralization here we construct deformable plate tectonic reconstructions for the south china block from 170 ma to the present using gplates the deformation starts with a nw se oriented shortening phase from 170 to 136 ma subsequently south china experienced two episodes of extension in the cretaceous during 136 118 ma and 100 80 ma respectively the cenozoic extension occurred mostly along the southeast continental margin including the east china sea shelf basin and rift basins in the northern south china sea margin and the taiwan margin segment the rifting was initiated nearly simultaneously along the continental margin at 65 ma and ceased at 34 30 ma the northern portion of the okinawa trough started rifting at 15 ma while the southern portion rifted in the last few million years the luzon volcanic arc thrusting onto the southeasternmost south china block since 6 5 ma caused the still active taiwan orogeny the predicted accumulated deformation at present day is characterized by overall shortening onshore with contraction factors mostly between 0 8 and 1 and extension offshore with stretching factors generally between 1 and 2 the central china orogen and taiwan orogen experienced more intense shortening relative to the interior south china by factors down to 0 6 the okinawa trough experienced intense stretching by factors up to 2 5 in its central part the intraplate deformation in the south china block is closely related to the subduction of the izanagi and pacific plates the jurassic and earliest cretaceous shortening was likely induced by trench advance and the extension during the cretaceous and the cenozoic was mostly driven by subduction retreat

directions and intensities of the earth s magnetic field during a reversal results from the permo triassic siberian trap basalts russia abstract an extensive palaeomagnetic study was carried out on an approximately 250 ma old reversed to normal transition of the earth s magnetic field emf recorded in 86 volcanic lava flows of the siberian trap basalts north siberia russia in addition to the investigation of the directional behaviour of the field 700 specimens a total of 298 specimens was subjected to thellier type palaeointensity determinations adding several modifications to the original thellier experiment such as tests for md tails and the additivity of partial thermoremanent magnetisation yields highly reliable palaeointensity estimates of the late permian early triassic emf transitional directions of the emf were obtained from 20 flows during the reversal a clustering of the virtual geomagnetic poles vgps is observed 15 flows palaeointensity estimates suggest that this feature is not an artifact due to rapid flow emplacement since the directional cluster is associated with a well defined increase in palaeointensity from 6 to 13 t subsequently the next vgps move towards the pole position of normal polarity departing in a sudden movement from normal polarity the vgps form a second directional cluster comprising the results of 14 flows this feature is interpreted as a post transitional excursion but lacks the characteristic intensity variation recorded during the first transitional cluster the rest of the section 41 flows is of normal polarity the characteristic features of this reversal low intensities and directional clustering during the reversal and an excursion shortly after the reversal were also observed in records of polarity transitions of younger age this suggests that the underlying reversal processes were similar the mean virtual dipole moment calculated for the stable normal part of the studied section yields a rather low value of 2 2 0 9 1022 am2 these findings confirm that the mesozoic dipole low extends at least down to the late permian early triassic the geomagnetic vgp dispersion was calculated for the stable normal part of the section and yields values similar to those for the last 5 ma considering that the intensity of the emf was considerably higher in this time interval than in the early triassic a direct relationship between intensity and secular variation seems unlikely

a reversal of the earth s magnetic field recorded in mid miocene lava flows of gran canaria paleointensities 1 an extensive paleointensity study was carried out on an approximately 14 1 myr old reverse to normal transition of the geomagnetic field a total of 188 samples from a volcanic sequence on gran canaria canary islands were subjected to thellier type paleointensity determinations the paleodirectional results of this sequence are reported by leonhardt et al 2002 a modified thellier technique which facilitates the recognition of md tails and the formation of new magnetic remanences with higher blocking temperatures than the actual heating step was used on the majority of the samples we obtained reliable paleointensity results for 35 of the 87 sampled lava flows in general the obtained field intensities are lower than expected for the mid miocene this observation is very likely related to a long term reduction of the field close to transitions very low paleointensities with values 5 t were obtained during an excursion preceding the actual transition and also close to significant changes of the local field directions these are interpreted as nondipolar components becoming dominant for short periods and provoking a rapid change of field directions during the transition 15 successive lava flows recorded similar local field directions corresponding to a cluster of virtual geomagnetic poles close to south america chronologically within this cluster the paleointensity increases from about 9 to 28 t followed by a decrease back to approximately 9 t this variation of paleointensity between lava flows with similar direction indicates independent records of the geomagnetic field and gives strong evidence for a stable transitional state that lasted a significant period

biomarkers of oligocene lacustrine source rocks beibuwan song hong basin junction offshore northern vietnam abstract highly oil prone source rocks containing sapropelic type i and mixed types i and iii kerogen are found in 233 m of the 500 m deep fully cored enreca 3 well drilled on bach long vi island located at the junction between the beibuwan and the song hong basins offshore northern vietnam the cored succession is made up entirely by oligocene deep lacustrine deposits the origin of the organic matter om in 62 samples is evaluated on the basis of gas chromatography mass spectrometry gc ms and gc ms ms om in 55 samples is sourced primarily from lacustrine organisms and contains abundant 4 methylsteranes tetracyclic polyprenoids tpp and lycopane and no markers for marine organic matter the proportion of triterpanes derived from angiosperms is low in most saturated fractions and only traces of gymnosperm diterpanes are detected in contrast all aromatic fractions have a high proportion of compounds having an origin from both gymnosperms and angiosperms very high concentrations of hopanoids in both fractions suggest significant bacterial alteration of the original om most samples have a high concentration of rare c31 diaromatic 8 14 secohopanes with a fluorene moiety low pristane phytane pr ph ratios indicate that anoxic suboxic bottom water conditions existed during om accumulation the presence of carotane gammacerane and traces of arylisoprenoids could indicate a stratified water column om in a few samples with lower than average hydrogen index hi is mainly of terrestrial origin with a higher proportion of c29 steranes diterpanes and oleanoids and lower concentrations of both saturated and aromatic hopanes higher pr ph a higher c34 isohopane ratio ihr34 and a lower homohopane index hhi indicate that this low hi om was originally deposited under more oxic conditions and subsequently transported to deeper water low sterane and hopane isomerization ratios show that no samples have reached the oil window some novel maturity parameters for immature lacustrine samples are proposed

eruptive history of the karoo lava flows and their impact on early jurassic environmental change this paper reports new paleomagnetic and geochronologic data from a 1500 m thick composite section belonging to the drakensberg group the thickest remnant of the karoo lavas in northern lesotho flow by flow analysis of paleomagnetic directions reveals twenty one magnetic directional groups dg corresponding to single eruptive events see and sixteen individual lava flows the new age determinations of lava flows range from 180 1 1 4 to 182 8 2 6 ma these data combined with previous results allow us to propose that the main part of the drakensberg group and the karoo intrusive complex dated around 181 183 ma may have been erupted over a period as short as 250 kyr and may have coincided with the two main phases of extinction in the early toarcian this scenario agrees well with the discontinuous rhythm of environmental and biotic perturbations in the late pliensbachian toarcian interval

does the permo triassic geomagnetic dipole low exist studies of absolute paleointensity have been conducted on specimens from permo triassic sills from the eastern areas of the kimberlite pipes sytikanskaya yubileinaya and aikhal and northwestern extrusions near noril sk city parts of the siberian platform a total of 341 specimens have been subjected to a modified thellier thellier technique which included partial thermoremanent magnetization checks and multidomain tail checks the paleomagnetic directions derived from the present set of experiments d 107 5 i 75 5 k 82 8 a95 5 3 n 10 sills for the eastern localities and d 95 1 i 71 8 k 35 2 a95 15 7 n 4 outcrops for the northwestern locality agree with the directions from previous studies the specimens from the northwestern sites noril sk did not provide any suitable result of absolute paleointensity the mean virtual dipole moment obtained from only the eastern localities has a value close to 6 01 1 45 10 22 am 2 which is over 50 higher than the results obtained by heunemann et al 2004 and shcherbakova et al 2005 on northwestern specimens the discrepancy could possibly be explained by the presence of multidomain grains in northwestern specimens where previous studies were undertaken which would reduce the paleointensity estimates at high temperatures however the present results lead us to conclude that 1 the geomagnetic field intensity at the permo triassic boundary was very close to the observed present day values and as a consequence a dipole low is not characteristic during this period of time 2 the mesozoic dipole low did not extend to the permo triassic boundary contrary to previous studies

paleomagnetism of trap intrusions east siberia implications to flood basalt emplacement and the permo triassic crisis of biosphere article history despite decades of concentrated studies large igneous provinces lips are still among the most enigmatic phenomena of the earth evolution among the myriad questions facing researchers the duration of eruptive magmatic activity and its distribution through time are probably the most mysterious ones although the accuracy of modern dating techniques offers relatively high resolution it is impossible to discriminate whether magmatic activity was more or less uniform or concentrated in few powerful outbursts consequently many trap related questions from their origin to possible impact on the biosphere still cannot be answered some of the above questions can be addressed with paleomagnetic data as have been effectively done in the case of the end cretaceous deccan traps the siberian traps are one of the largest lips in the phanerozoic and are thought by some to be the triggering event for the end permian mass extinction we conducted a paleomagnetic study of trap intrusions along two long profiles in the eastern part of the province and found that most site mean directions are grouped several times tighter than is common for the data on thick lava series and dyke swarms similar over grouping is found in other parts of the siberian trap province too we argue that this phenomenon is the most likely related to nearly simultaneous emplacement of trap intrusions over areas of several ten to few hundred kilometers in dimension for few millenniums or even faster moreover such brief events account for all or nearly all magmatism in each area how such events correlate over the entire siberian lip however remains an open question still our data together with paleomagnetic results on thick lava series in siberia strongly indicate that magmatic activity consisted of a number of brief pulses in comparison to the other lips the siberian one is underlain by the thickest succession of carbonates evaporites and coal bearing clastics that are capable of producing huge amount of green house and poisonous gases we hypothesize that these very fast injections of magma into thick underlying sediments and the unique geological setting of the siberian lip are the major reasons for the permo triassic mass extinction being

scintillation producing fresnel scale irregularities associated with the regions of steepest tec gradients adjacent to the equatorial ionization anomaly 1 using ground based gps and digital ionosonde instruments we have built up at latitudes of the equatorial ionization anomaly eia in the brazilian sector a time evolving picture of total electron content tec l band amplitude scintillations and f region heights and we have investigated likely reasons for the occurrence or suppression of equatorial scintillations during the disturbed period of 18 23 november 2003 during the prestorm quiet nights scintillations are occurring postsunset as expected however during the storm time period their spatial temporal characteristics and intensity modify significantly owing to the dramatic changes in the ionospheric plasma density distribution and in the temporal evolution of tec the two dimensional maps showing both tec and amplitude scintillations revealed strong evidence of turbulences at the fresnel length causing scintillations concurrent with those regions of steepest tec gradients adjacent to the crests of the eia the largest density gradients have been found to occur in an environment of increased background electron density and their spatial distribution and location during the disturbed period may differ significantly from the magnetic quiet night pattern however in terms of magnitude the gradients at equatorial and low latitudes appear to not change during both magnetic quiet and disturbed conditions the scenarios for the formation or suppression of scintillation producing fresnel scale irregularities during the prestorm quiet nights and disturbed nights are discussed in view of different competing effects computed from numerical simulation techniques

thermospheric wind during a storm time large scale traveling ionospheric disturbance 1 a prominent large scale traveling ionospheric disturbance lstid was observed in japan during the major magnetic storm dst 358 nt of 31 march 2001 it was detected as enhancements of the 630 nm airglow and fof2 gps tec variations and a decrease in f layer virtual height at 1700 1900 ut 0200 0400 lt it moved equatorward with a speed of 600 m s the decrease in the f layer height was also detected by the mu radar at shigaraki thermospheric wind variations were observed by the mu radar through ion drift measurement and by a fabry perot interferometer fpi through a doppler shift of the 630 nm airglow line at shigaraki the wind data show a turn of the meridional wind from 94 m s equatorward to 44 m s poleward during the lstid indicating that an intense poleward wind in the thermosphere passed over shigaraki as an atmospheric gravity wave and caused the observed ionospheric features of the lstid intense poleward wind was also detected at mesospheric altitudes 95 100 km by the mu radar through meteor echoes and by the fpi through the 558 nm airglow with a delay of 2 hours from the thermospheric wind indicating downward phase progression of the wave generation of the observed poleward wind in the auroral zone was investigated using magnetic field data and auroral energy input estimated by the assimilative mapping of ionospheric electrodynamics amie technique we suggest that simple atmospheric heating and or the lorentz force in the auroral zone do not explain the observed poleward wind enhancement

estimating daytime vertical exb drift velocities in the equatorial f region using ground based magnetometer observations 1 the daytime equatorial electrojet is a narrow band of enhanced eastward current flowing in the 100 to 120 km altitude region within 2 latitude of the dip equator a unique way of determining the daytime strength of the electrojet is to observe the difference in the magnitudes of the horizontal h component between a magnetometer placed directly on the magnetic equator and one displaced 6 to 9 degrees away the difference between these measured h values provides a direct measure of the daytime electrojet current and in turn the magnitude of the vertical exb drift velocity in the f region ionosphere this paper discusses a recent study that has established the quantitative relationship between the vertical exb drift velocity in the ionospheric f region and the daytime strength of the equatorial electrojet in the south american west coast longitude sector

novel c26 tetracyclic degraded bicadinanes in oil sands from the haitoubei maichen sag of the beibuwan basin south china sea abstract three c 26 tetracyclic terpanes were detected in the saturated hydrocarbon fractions of oil sand samples especially rich in bicadinanes w t and r from the oligocene huizhou formation in the xw 1 well in the haitoubei maichen sag of the beibuwan basin their mass spectra show molecular ions of the three tetracyclic terpanes at m z 358 and their key fragment ions at m z 343 m 15 and m z 315 due to loss of an isopropyl group these characteristics are very similar to that of c 30 cis cis trans w and trans trans trans t bicadinanes in addition the relative abundances of the c 26 tetracyclic terpanes show an excellent positive correlation with the c 30 bicadinanes w and t in 27 oil sand samples therefore the three c 26 tetracyclic terpanes are tentatively identified as degraded bicadinanes which like bicadinanes may indicate input from dammar resins and can be used to discriminate the origin of crude oils

a climatology of f region gravity wave propagation over the middle and upper atmosphere radar by observing the ionospheric f region simultaneously in multiple beams with the middle and upper atmosphere radar we have been able to track the passage of gravity waves and measure their propagation characteristics here we develop a climatology of wave propagation based on the observation of 58 daytime experiments conducted during 1986 1994 the thermosphere seems to be continuously swept by waves detectable by an incoherent scatter radar these waves generally come for hours on end from a consistent or slowly varying direction which can be any direction on a given day statistically the waves show a moderate preference for southward travel with this preference being reduced or shifted to southeastward travel during disturbed times on average the horizontal phase trace speed remains near 240 m s for all periods inspected 40 130 min this speed matches the behavior expected for lossless waves with 150 200 km vertical wavelength we find small variability in this relation for different times of day seasons solar and magnetic conditions and directions of wave travel though waves on disturbed days seem to travel moderately faster on solar minimum mornings

paleogene structural development of the northern song hong basin and adjacent areas implications for the role of extrusion tectonics in basin formation in the gulf of tonkin abstract the song hong basin situated at the distal part of the ailaoshan red river shear zone asrrsz holds important information on the role of extrusion tectonics in the marginal basin development in the south china sea based on an extensive dataset of 2 and 3 d seismic and stratigraphic information from 27 exploration wells the paleogene structural evolution of the northern song hong basin and adjacent areas has been studied in detail this study proposes a new paleogene structural development model of the study area eocene oligocene rifting in the northern song hong basin was driven by left lateral shearing from the asrrsz associated with a combined motion of clockwise rotation and translation of the indochina block which allowed extension along the restraining bend geometry of the basin s eastern margin a structural high separates the song hong basin from the beibuwan basin inhibiting significant strike slip displacement transfer from the asrrsz into rifting in the beibuwan basin strike slip displacement from the asrrsz is maintained further south to the east vietnam boundary fault segment thus extension of the beibuwan qiongdongnan and phu khanh basins were the result of the interplay between extrusion and slab pull tectonics during the end of the oligocene reduced extrusion of indochina caused minimal rotation of the block and the remaining left lateral displacement along the asrrsz was absorbed into inversion around the junction between the song hong and beibuwan basins

a minimum upb age for siberian flood basalt volcanism abstract establishing an accurate and precise age for siberian flood basalt volcanism is of great importance in evaluating causes for the unequaled mass extinction of flora and fauna at the permian triassic boundary we report a new minimum u pb age obtained from zircon and baddeleyite from the mineralized noril sk i intrusion that cuts the lower third of this rapidly deposited 3500 m thick volcanic sequence near noril sk this 251 2 0 3 2 ma age is within analytical error of the shrimp u pb age for zircon from the permian triassic boundary at meishan south china 251 1 3 6 ma 2 and confirms siberian basaltic volcanism as a possible contributor to the mass extinction

structure and significance of c30 4 methyl steranes in lacustrine shales and oils abstract the structure of the abundant c 30 4 methyl steranes of ancient freshwater lacustrine sediments and derived oils is of interest as their precursors the 4 methyl and in particular 4 23 24 trimethyl sterols dinosterols are reported to be specific to dinoflagellates this study employs a novel liquid crystal gc phase combined with gc ms and gc ms ms to separate and characterise mixtures of c 30 4 methyl sterane standards not resolvable on non polar phases this technique is then applied to identify the c 30 4 methyl steranes in an ancient freshwater sediment a freshwater lacustrine and a marine derived oil a comparison is also made with the 4 methyl steranes in marine sediments containing varying amounts of dinoflagellate cysts the c 30 4 methyl steranes of the freshwater lacustrine samples have been shown to possess a 4 methyl 24 ethylcholestane structure while both 4 methyl 24 ethylcholestanes and 4 23 24 trimethyl 5 h cholestanes dinosteranes were found in the marine dinoflagellate rich sediments while still indicative of dinoflagellates 4 methyl 24 ethyl sterols are generally not the major dinoflagellate sterol and alternative explanations for the abundance of 4 methyl 24 ethylcholestanes in ancient lacustrine sediments should be considered possibly ancient freshwater dinoflagellates synthesised principally the 4 methyl 24 ethyl form alternatively a source from an unrecognized algal class is possible while a source from bacteria which are known to synthesise certain 4 methylsterols is discussed

southern hemisphere ionosphere and plasmasphere response to the interplanetary shock event of 29 31 october 2003 1 we analyze the effects on the southern hemisphere ionosphere and plasmasphere due to the 29 31 october 2003 geomagnetic storms the so called series of halloween storms solar wind data from ace and ionospheric data from the gps global position system ground and leo low earth orbit receivers the topex poseidon altimeter the image fuv camera and the dmsp drift meter are used to understand the ionospheric dynamics as a function of the storm phase the detailed structure of the ionosphere has been obtained using tomographic reconstruction applied to data from both ground and space based gps receivers the tomographic approach using leo observations of signals received from gps satellites above the leo s horizon allows us to investigate the topside ionospheric and plasmaspheric density distribution in more detail than can be obtained using ground based gps receivers this is because with ground based receivers the higher topside ionosphere and plasmasphere contribute only a small fraction to the total electron content tec and so the measurements are dominated by the ionospheric structure at the f2 peak in contrast the australian leo satellite fedsat which has been used for this study orbits at 800 km altitude well above the f2 peak and hence the tec measured is primarily due to the upper topside ionosphere and plasmasphere this paper presents the tomographically reconstructed topside ionosphere and plasmasphere electron density distributions using leo observations the temporal and regional maps of tec and the image fuv data show that the storm that commenced on 29 october dramatically decreased the plasma density in the southern hemisphere middle and high latitudes the region remained depleted of plasma for more than 24 hours until 31 october when the second severe storm began topex poseidon data shows a daytime localized density enhancement occurred above the middle of the pacific ocean these results show large interhemispheric and longitudinally narrow storm time structure in the ionosphere and topside ionosphere plasmasphere

dipolar reversal states of the geomagnetic field and core mantle dynamics palaeomagnetic records from lavas suggest that at least two specific inclined dipolar field configurations have dominated the reversal process for the past ten million years these long lived states provide a way to explain directional rebounds aborted reversals and the recording in sediments of what appear to be preferred longitudinal paths of the virtual geomagnetic pole the polar orientations correlate with near radial flux concentrations recognizable when today s field is stripped of its axial dipole and with lower mantle seismic anomalies suggesting a tie to deep earth dynamics

a statistical study of large scale traveling ionospheric disturbances observed by gps tec during major magnetic storms over the years 2003 2005 1 in this paper we plot two dimensional total electron content tec perturbation maps and investigate the statistical characteristics of large scale traveling ionospheric disturbances lstids during major magnetic storms from 2003 to 2005 the tec data were obtained from more than 600 gps receivers in north america within the geographical latitudes of 25 n 55 n we found a total of 135 cases of lstids with amplitudes of up to 3 5 tecu and a maximum front width of 4000 km the mean value of periods horizontal velocities and azimuths are 1 8 h 300 m s and 187 7 west of south respectively the mean velocity is obviously slower than that observed at lower latitudes such as japan of all the 135 lstid events 35 cases 26 occurred in the nighttime with their possible source within the region of north america according to the variation of magnetic h component observed in this region in addition the occurrence of lstids peaks at 1200 lt and at 1900 lt it is also pointed out that the ut dependence of the occurrence of auroral geomagnetic disturbances plays a major role in the forming of ut and lt dependence of the occurrence of lstids observed at midlatitudes

paleomagnetism of the siberian traps new data and a new overall 250 ma pole for siberia the flood basalt province in siberia is one of the largest in the world but the number of reliable paleomagnetic data on these volcanics is still limited we studied lava flows and trap related intrusions from two areas in the north and west of the siberian platform a dual polarity characteristic component was isolated from most samples with the aid of stepwise thermal and alternating field demagnetization we then compiled all published paleomagnetic data on the siberian traps that have been obtained according to modern standards also included are presumably trap related overprint directions in paleozoic rocks although these overprints and trap results may locally differ the corresponding mean poles based on remagnetized sediments and volcanics show excellent overall agreement and justify pooling of both data types several ways of data grouping were attempted the trap mean pole proved to be rather insensitive to statistical treatment irrespective of the averaging procedure used the overall mean poles for the siberian traps nsp2 55 1 n 147 0 e n 8 k 123 a95 5 0 or nsp4 57 2 n 151 1 e n 8 k 192 a95 4 0 differ slightly but significantly from the coeval mean poles of baltica torsvik 2001 van der voo r and torsvik t h the quality of the european permo triassic paleopoles and its impact on pangea reconstructions in timescales of the paleomagnetic field j e t channell d v kent w lowrie and j g meert eds agu geophys monogr 2004 135 29 42 we consider possible causes for this difference and conclude that it could be explained either by persistent non dipole terms in the permo triassic geomagnetic field or widespread inclination shallowing in the european data

palaeosecular variation over the past 5 myr based on a new generalized database summary a generalized database of global palaeomagnetic data from 3719 lava flows and thin dykes of age 0 5 ma has been constructed for use with a relational database management system the database includes all data whose virtual geomagnetic poles vgp lie within 45 of the spin axis and can be used for studies of palaeosecular variation and for geomagnetic field modelling because many of these data were collected and processed more than 15 20 years ago each result has been characterized according to the demagnetization procedures carried out analysis of these data in terms of the latitude variation of the angular dispersion of vgps palaeosecular variation from lavas strongly suggests that careful data selection is required and that many of the older studies may need to be redone using more modern methods differences between the angular dispersions for separate normal and reverse polarity data sets confirm that many older studies have not been adequately cleaned magnetically therefore the use of the database for geomagnetic field modelling should be carried out with some caution using a vgp cut off angle that varies with latitude the best data set consists of 2636 results that show a smooth increase of vgp angular dispersion with latitude model g for palaeosecular variation which is based on modelling of the antisymmetric dipole and symmetric quadrupole dynamo families provides a good fit to these results

the steens mountain oregon geomagnetic polarity transition 2 field intensity variations and discussion of reversal models we carried out an extensive paleointensity study of the 15 5 0 3 m y miocene reversed to normal polarity transition recorded in lava flows from steens mountain south central oregon one hundred eighty five samples from the collection whose paleodirectional study is reported by mankinen et al this issue were chosen for paleointensity investigations because of their low viscosity index high curie point and reversibility or near reversibility of the strong field magnetization curve versus temperature application of the thellier stepwise double heating method was very successful yielding 157 usable paleointensity estimates corresponding to 73 distinct lava flows after grouping successive lava flows that did not differ significantly in direction and intensity we obtained 51 distinguishable complete field vectors of which 10 are reversed 28 are transitional and 13 are normal the record is complex quite unlike that predicted by simple flooding or standing nondipole field models it begins with an estimated several thousand years of reversed polarity with an average intensity of 31 5 8 5 t about one third lower than the expected miocene intensity this difference is interpreted as a long term reduction of the dipole moment prior to the reversal when site directions and intensities are considered truly transitional directions and intensities appear almost at the same time at the beginning of the transition and they disappear simultaneously at the end of the reversal large deviations in declination occur during this approximately 4500 1000 year transition period that are compatible with roughly similar average magnitudes of zonal and nonzonal field components at the site the transitional intensity is generally low with an average of 10 9 4 9 t for directions more than 45 away from the dipole field and a minimum of about 5 t the root mean square of the three field components x y and z are of the same order of magnitude for the transitional field and the historical nondipole field at the site latitude however a field intensity increase to pretransitional values occurs when the field temporarily reaches normal directions which suggests that dipolar structure could have been briefly regenerated during the transition in an aborted attempt to reestablish a stationary field changes in the field vector are progressive but jerky with at least two and possibly three large swings at astonishingly high rates each of those transitional geomagnetic impulses occurs when the field intensity is low less than 10 t and is followed by an interval of directional stasis during which the magnitude of the field increases greatly for the best documented geomagnetic impulse the rapid directional change corresponds to a vectorial intensity change of 6700 2700 nt yr 1 which is about 15 50 times larger than the maximum rate of change of the nondipole field observed during the last centuries the occurrence of geomagnetic impulses seems to support reversal models assuming an increase in the level of turbulence within the liquid core during transitions the record closes with an estimated several thousand years of normal polarity with an average intensity of 46 7 20 1 t agreeing with the expected miocene value however the occurrence of rather large and apparently rapid intensity fluctuations accompanied by little change in direction suggests that the newly reestablished dipole was still somewhat unstable

an absolute palaeointensity record from soh1 lava core hawaii using the microwave technique absolute palaeointensity results were obtained from 392 samples 166 of 241 flows from the upper 779 m of the scientific observation hole 1 soh1 basalt core kilauea volcano hawaii using the microwave palaeointensity technique based on k ar dates and a previously published age model this covers the last 45 ka thus giving a high resolution record of geomagnetic intensity in hawaii comparisons with other hawaiian absolute palaeointensity data show similar trend of higher intensity than present day for the last 3 ka and then a general decrease in intensity over the last 45 ka though this study reports consistently lower palaeointensity values direct comparison with previous thellier data from the soh1 core shows some discrepancies between the two methods with the thellier data yielding generally higher palaeointensity estimates than the microwave data in view of these discrepancies between the two methods the introduction of raw palaeointensity data into the public domain is suggested

intensity of the earth s magnetic field evidence for a mesozoic dipole low the variation of the strength of the earth s magnetic field throughout geological time is known only poorly large uncertainties spoil indirect paleointensity determinations based on magnetic anomaly amplitude or remanence of sedimentary rocks even when paleointensity data are obtained from direct thermomagnetic studies of magmatic units fundamental problems related to the actual nature of the primary remanence and to the effects of different cooling rates may result in erroneous determinations these uncertainties combined with well known experimental difficulties can explain the large scatter in paleointensity data reported in most previous review papers because experimental difficulties are more rigourously dealt with using the thellier method which also offers some opportunities to minimize some fundamental uncertainties we carried out a compilation of all triassic and younger paleointensity determinations made using this method this selected data set indicates the occurrence of large long term changes of the geomagnetic dipole strength with time the average dipole strength seems to have been approximately constant since late cretaceous time but a dipole strength only one third of the cenozoic value prevailed during most of mesozoic time following a period of larger strength ending possibly during early jurassic times the mesozoic dipole low may be correlated with a cessation of relative motion between the geomagnetic axis and the mantle the terrestrial dynamo seems therefore to exhibit different long term stable states which are probably controlled by the thermal structure in the lowermost mantle

the altitude extension of the mid latitude trough and its correlation with plasmapause position 1 tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density in an altitude versus geographic latitude grid at a specified longitudinal sector the method which involves monitoring the total electron content tec of the ionosphere using signals transmitted from the global positioning system gps has the ability to reveal the detailed structure of the ionosphere including the mid latitude trough the tomographic reconstruction of ionospheric electron density structures are performed at different specific longitudinal sectors both in the northern and southern hemisphere at the same time the plasmapause position is estimated from image euv images and mapped onto tomographic images the simultaneous location of the altitude extension of the mid latitude trough and the plasmapause position are essentially co located

comparison of the coe thellier thellier and microwave palaeointensity techniques using high titanium titanomagnetites results from a tertiary basaltic intrusion from the sydney basin new south wales abstract conventional thellier and microwave mw palaeointensity experiments accompanied by rock magnetic tests were conducted on samples from an early tertiary ca 49 ma basaltic intrusion the peats ridge pr basalt from the sydney basin thermomagnetic and low temperature susceptibility measurements suggest that the dominant magnetic mineral is ti enriched titanomagnetite tm65 tm50 and hysteresis results indicate that the majority of samples exhibit psd like behaviour some samples show evidence of alteration during laboratory heating but only at temperatures in excess of 400 c no alteration is observed in the dominant temperature range 70 300 c used for calculation of palaeointensities stepwise thermal demagnetisation studies reveal single component after removal of a small viscous reverse polarity magnetisations in all samples with a mean characteristic remanence chrm direction of d i 197 60 95 5 k 62 coe thellier thellier ctt experiments yielded a high success rate with 68 of samples conforming to standard acceptance criteria microwave mw palaeointensity experiments predominantly using the perpendicular applied field technique produced a greater success rate of 82 mean palaeointensities of 27 1 4 4 t n 21 and 27 4 4 0 t n 28 were obtained from the ctt and mw techniques respectively these means could not be distinguished statistically and the respective quality indicators were similar these results suggest that the new microwave technique for calculating palaeointensities is in this case equivalent to the well established ctt technique this is an intuitive outcome given that rock magnetic analyses suggest that alteration does not occur below the curie temperature of the samples our results therefore provide a positive test for the equivalence of the mw and ctt techniques the virtual dipole moment vdm value for the intrusion is 4 7 0 7 10 22 am 2 suggesting that the dipole field was approximately 59 of the present day value at ca 49 ma this provides a valuable data point from the southern hemisphere for a sparsely covered time period in the global palaeointensity database

on the dynamics of large scale traveling ionospheric disturbances over europe on 20 november 2003 ionospheric disturbances often associated with geomagnetic storms may cause threats to radio systems used for communication and navigation one example is the super storm on 20th november 2003 when plenty of strong and unusual perturbations were reported this paper reveals additional information on the dynamics in the high latitude ionosphere over europe during this storm here analyses of wavelike travelling ionospheric distrubances tids over europe are presented based on estimates of the total electron content tec derived from ground based global navigation satellite system gnss measurements these tids are ionospheric signatures of thermospheric surges initiated by space weather events the source region of these tids is characterized by enhanced spatial gradients tec depression strong uplift of the f2 layer the vicinity of the eastward auroral electrojet and strong aurora e layers joule heating is identified as the most probable driver for the tids observed over europe during 20th november 2003 the sudden heating of the thermosphere leads to strong changes in the pressure and thermospheric wind circulation system which in turn generates thermospheric wind surges observed as tid signatures in the tec either the dissipation of the eastward auroral electrojet or particle precipitation are considered as the source mechanism for the joule heating in the course of the storm the tec observations show a southward shift of the source region of the tids these meridional dislocation effects are obviously related to a strong compression of the plasmasphere the presented results demonstrate the complex interaction processes in the thermosphere ionosphere magnetosphere system during this extreme storm

paleomagnetism of the early triassic semeitau igneous series eastern kazakstan 1 paleomagnetic results obtained from the early triassic semeitau igneous series sis yield a high quality pole for eastern kazakstan that is concordant with reference poles for siberia and europe strongly supporting the hypothesis that kazakstan was already joined with eurasia at this time of the 25 sites that were measured data were straightforward for 20 sites 2 of which recorded normal polarity and 18 of which recorded reverse 5 sites were discarded because of severe overprinting unstable demagnetizations or extremely scattered within site directions combining sites judged to be the same cooling unit and taking the average of 15 cooling units of equal weight we calculated a pole located at 56 n 139 e n 15 k 24 6 95 7 9 for the sis we consider this pole to be reliable the sampling of temporally spaced extrusives and more slowly cooled intrusives and the presence of both polarities strongly suggest that this pole averages secular variation the 40ar 39ar determinations on sanidine crystals from two extrusive units yielded highly consistent ages of 248 2 0 5 and 248 8 0 5 ma comparison of our pole for the sis with the siberian reference pole shows relative translation 8 10 and rotation 1 16 that are indistinguishable from zero at 95 confidence this result fails to confirm hypothesized post permian rotation of the siberian craton relative to its margins and provides no evidence for left lateral motion on the east west shear zones in which the semeitau is located the similarity of ages between the sis and the siberian traps supports speculation of a genetic relationship between the two

multiradar observations of the polar tongue of ionization 1 we present a global view of large scale ionospheric disturbances during the main phase of a major geomagnetic storm we find that the low latitude auroral and polar latitude regions are coupled by processes that redistribute thermal plasma throughout the system for the large geomagnetic storm on 20 november 2003 we examine data from the high latitude incoherent scatter radars at millstone hill sondrestrom and eiscat tromso with superdarn hf radar observations of the high latitude convection pattern and dmsp observations of in situ plasma parameters in the topside ionosphere we combine these with north polar maps of stormtime plumes of enhanced total electron content tec derived from a network of gps receivers the polar tongue of ionization toi is seen to be a continuous stream of dense cold plasma entrained in the global convection pattern the dayside source of the toi is the plume of storm enhanced density sed transported from low latitudes in the postnoon sector by the subauroral disturbance electric field convection carries this material through the dayside cusp and across the polar cap to the nightside where the auroral f region is significantly enhanced by the sed material the three incoherent scatter radars provided full altitude profiles of plasma density temperatures and vertical velocity as the toi plume crossed their different positions under the cusp in the center of the polar cap and at the midnight oval polar cap boundary greatly elevated f peak density 1 5e12 m 3 and low electron and ion temperatures 2500 k at the f peak altitude characterize the sed toi plasma observed at all points along its high latitude trajectory for this event sed toi f region tec 150 1000 km was 50 tecu both in the cusp and in the center of the polar cap large upward directed fluxes of o 1 e14 m 2 s 1 were observed in the topside ionosphere

paleomagnetism and dating of a thick lava pile in the permian bakaly formation of eastern kazakhstan regularities and singularities of the paleomagnetic record in thick lava series abstract paleomagnetic results on thick lava series are among the most important sources of information on the characteristics of ancient geomagnetic fields most paleo secular variation data from lavas psvl are of late cenozoic age there are far fewer results from lavas older than 5 ma the central asia orogenic belt that occupies several million square kilometers in asia is probably the world s largest area of paleozoic volcanism and is thus an attractive target for psvl studies we studied a ca 1700 m thick lava pile in eastern kazakhstan of early permian age magmatic zircons successfully separated from an acid flow in this predominantly basaltic sequence yielded an early permian age of 286 3 3 5 ma oriented samples were collected from 125 flows resulting in 88 acceptable quality flow means n 4 samples radius of confidence circle 95 15 of the high temperature magnetization component the uniformly reversed component is pre tilting and arguably of a primary origin the overall mean direction has a declination 242 0 and an inclination 56 2 k 71 5 95 1 8 n 88 sites pole at 44 1 n 160 6 e a95 2 2 our pole agrees well with the early permian reference data for baltica in accord with the radiometric age of the lava pile and geological views on evolution of the western part of the central asia orogenic belt the new early permian result indicates a comparatively low level of secular variation especially when compared to psvl data from intervals with frequent reversals still the overall scatter of dispersion estimates that are used as proxies for sv magnitudes elongation values and elongation orientations for psvl data is high and cannot be fitted into any particular field model with fixed parameters both observed values and numerical simulations indicate that the main cause for the scatter of form parameters elongation values and elongation orientations is the too small size of collections dispersion estimates concentration parameter and standard angular deviation are more robust and their scatter stems from other sources which may include non stochastic features of datasets like clusters loops etc or non stationary behavior of secular variation magnitude over time intervals of many million years

palaeointensity record through the lower mammoth reversal from the waianae volcano hawaii the normal to reverse lower mammoth reversal 3 33 ma has been recorded in several sequences of lava from the waianae volcano the island of oahu hawaii 137 samples from 29 flows from the pu u paheehee section have been the subject of a palaeointensity study using the microwave technique duplicate sister samples from the directional study of herrero bervera and valet earth planet sci lett 171 1999 139 148 were used microwave demagnetisation was carried out on all samples and the directions compared to the published flow mean directions microwave palaeointensity experiments were carried out on all accepted samples using the 8 2 ghz and 14 ghz microwave systems the perpendicular applied field palaeointensity method and a coe analogue method were used eighty four samples from 24 flows gave acceptable palaeointensity results the results indicate that the geomagnetic field was low mean 5 9 1 3 t n 7 prior to the transitional directions during the first stage of the reversal the field remains low results however could only be obtained from three transitional flows the field then strongly recovers with very high intensity 70 t and reversed direction after this the intensity decreases before the field becomes transitional again for a cluster of four flows the field does not reduce as much as previously rather it is about twice the pre reversal intensity for the final section of reversed flows the intensity is more than twice the pre reversal mean value 15 1 5 9 t n 7 whilst some similarities are seen between this reversal and other reversals of different ages and locations there is not enough data at present to say whether there is any systematic behaviour

some global features of palaeointensity in geological time summary a global palaeointensity data base was constructed from all published data from volcanic rocks in geological time older than 0 03 ma the data base contains a total of 1123 flow mean data retrieved from 83 original papers various features of the earth s dipole moment were examined from the data which are based on thellier and shaw methods long term variation of the earth s dipole moment seems to have existed in the past 300 ma with a broad minimum at 120 180 ma as suggested by prevot et al 1990 however due to limited site distribution we cannot regard this mesozoic dipole low as being completely established precambrian palaeointensity data are still insufficient to conclude any long term variation in this time range although the geodynamo processes of moderate magnitude definitely existed in the early time of the earth s history the 2 test was applied to the distribution of the virtual dipole moment for the past 5 ma in which the transitional data were excluded the results indicate that the distribution of virtual dipole moment is better represented by a log normal distribution rather than a normal distribution and this tendency seems to be true for the past 20 ma the relation of mean palaeointensity versus palaeomagnetic colatitude was examined for the past 10 ma for the data excluding transitions the relation is concordant with a theoretical curve from a geocentric axial dipole this reconfirms that the dipole field was dominant in the past geomagnetic field which is the dipole hypothesis in palaeomagnetism on the other hand the virtual dipole moment is much smaller for transitional palaeomagnetic fields and a virtual geomagnetic pole lower than 45 seems to be a reasonable criterion to be categorized as a transition the mean dipole moment for the pole latitude of 30 n 50 n band is larger than that for 30 s 50 s indicating that there might have been a persistent asymmetry of palaeointensity between normal and reversed states or some kind of geometrical asymmetry between the northern and southern hemispheres

superposed epoch analysis of the dayside ionospheric response to four intense geomagnetic storms 1 prompt daytime ionospheric responses are presented for the following four intense geomagnetic storms 29 october 2003 30 october 2003 20 november 2003 and 7 november 2004 we perform a superposed epoch analysis of the storms by defining the start time of the epoch when the kan lee interplanetary electric field proportional to the reconnection electric field first reaches 10 mv m during a period of continuously southward bz measurements from the gps receiver onboard the champ satellite at 400 km altitude indicate significant low to middle latitude daytime total electron content tec increases above the satellite within 1 2 h of the defined start time for three of the storms 1400 local solar time the 20 november 2003 data follow a different pattern the largest tec increases appear several hours 5 7 following the interplanetary magnetic field bz event onset tec data obtained from ground based gps receivers for the november 2003 storm tend to confirm a late tec increase for this storm at 1400 lt estimates of vertical plasma uplift near the equator at jicamarca longitudes 281 e using the dual magnetometer technique suggest that variability of the timing of the tec response is associated with variability in the prompt penetration of electric fields to low latitudes it is also found that for the november 2003 magnetic storm the cross correlation function between the sym h index and the interplanetary electric field reached maximum correlation with a lag time of 4 h such a large lag time has never been noted before the long delays of both the ionosphere and magnetosphere responses need to be better understood

petroleum generation migration and entrapment in the zhu 1 depression pearl river mouth basin south china sea abstract analysis of crude oils from several fields in and near the huizhou sag zhu 1 depression pearl river mouth basin provides an excellent demonstration of inferring petroleum generation migration and entrapment in areas where drilling encounters hydrocarbons but fails to penetrate the effective generative sequence this paper illustrates the integration of geochemical geophysical and geological interpretations to develop a model of petroleum generation migration and entrapment the zhu 1 depression is one of three subbasins in the pearl river mouth basin sediment fill within the subbasin consists of paleogene synrift units and miocene to recent postrift deposits although drilling in the zhu 1 s huizhou sag and on the adjacent dongsha massif has netted numerous oil discoveries since the early 1980 s it has not encountered any effective or potential source rocks within the penetrated sections however interpretation of the systematic variations in crude oil chemistry within the regional geologic and structural framework has been invaluable in inferring source attributes and delineating location and distribution of the unpenetrated probable source the signatures resulting from genetic and alteration processes suggest that high wax oils were generated in mature lacustrine source facies of the synrift sequence and were expelled into a tightly sealed massive sandstone carrier system they migrated south southeast toward the dongsha massif were entrapped to spill point in traps along the migration route and were altered increasingly within the successively shallower and cooler reservoirs on the massif

microwave paleointensities indicate a low paleomagnetic dipole moment at the permo triassic boundary the quantity of igneous material comprising the siberian traps provides a uniquely excellent opportunity to constrain earth s paleomagnetic field intensity at the permo triassic boundary there remains however a contradiction about the strength of the magnetic field that is exacerbated by the limited number of measurement data to clarify the geomagnetic field behavior during this time period for the first time a microwave paleointensity study has been carried out on the permo triassic flood basalts in order to complement existing datasets obtained using conventional thermal techniques samples which have been dated at 250 ma of the permo triassic trap basalts from the northern extrusive maymecha kotuy region and the southeastern intrusive areas of the sytikanskaya and yubileinaya kimberlite pipes localities on the siberian platform are investigated these units have already demonstrated reliable paleomagnetic directions consistent with the retention of a primary remanence furthermore scanning electron microscope analysis confirms the presence of iron oxides likely of primary origin microwave thellier type paleointensity experiments izzi protocol with partial thermoremanent magnetization checks are performed on 50 samples from 11 sites of which 28 samples from 7 sites provide satisfactory paleointensity data the samples display corresponding distinct directional components positive ptrm checks and little or no zig zagging of the arai or zijderveld plot providing evidence to support that the samples are not influenced by lab induced alteration or multi domain behavior the accepted microwave paleointensity results from this study are combined with thermal thellier type results from previously published studies to obtain overall estimates for different regions of the siberian traps the mean geomagnetic field intensity obtained from the samples of the northern part is 13 4 12 7 t maymecha kotuy region whereas from the southeastern part is 17 3 16 5 t sytikanskaya kimberlite pipe and 48 5 7 3 t yubileinaya kimberlite pipe suggesting that the regional discrepancy is probably due to the insufficient sampling of geomagnetic secular variation and thus multiple localities need to be considered to obtain an accurate paleomagnetic dipole moment for this time period it demonstrates that the overall mean paleointensity of the siberian traps is 19 5 13 0 t which corresponds to a mean virtual dipole moment of 3 2 1 8 1022 am2 results indicate that the average magnetic field intensity during permo triassic boundary is significantly lower by approximately 50 than the present geomagnetic field intensity and thus it implies that the mesozoic dipole low might extend 50 myr further back in time than previously recognized

palaeointensity and palaeomagnetic study of cretaceous and palaeocene rocks from western antarctica summary a combined palaeodirectional and palaeointensity study of a representative collection of plutonic rocks from the antarctic peninsula batholith from the western part of the antarctic peninsula near the ukrainian antarctic base academik vernadsky were carried out petrographically the collection includes gabbros diorites and quartz diorites tonalities granodiorites and granites the ages of igneous complex emplacement vary from 50 to 117 ma with most of the rocks belonging to the cretaceous normal superchron the characteristic remanent magnetizations were isolated by stepwise thermal demagnetization over the temperature interval 440 590 c and their intensities amount to 95 per cent of the nrm the geographic positions of palaeopoles do not contradict the key poles of the antarctic peninsula between 90 and 60 ma a significant part of the collection was subjected to coe modified thellier palaeointensity experiments with the ptrm checks which yielded seven reliable palaeointensity determinations for seven different locations the obtained vdms are relatively low for all sites being on average about half of the present day vdm the analysis of available palaeointensity data for the cretaceous miocene and middle jurassic indicates the existence of strong correlations between the mean vdm and vdm scatter versus the rate of reversals however due to the shortage of data the correlations are not significant at the 5 per cent significance level

paleomagnetic volcanic data and geometric regularity of reversals and excursions mostly on the basis of paleomagnetic sedimentary data it has been suggested that maps of virtual geomagnetic poles vgps corresponding to directions of the magnetic field at each site tend to fall along american and asian longitudes during reversals and excursions such geometric regularity in transitional fields may indicate that the core and mantle are dynamically coupled however studies of paleomagnetic lava data have thus far failed to show any pattern in transitional fields in this paper we examine a paleomagnetic lava database covering reversals and excursions which have occurred over the last 20 myr volcanic eruptions occur sporadically thus we normalize the data to account for the fact that reversal and excursional events at the various sites are recorded by different numbers of intermediate directions but we prefer not to use averaging methods of previous investigators who discarded or combined directions when they appeared to be similar we find that volcanic data give intermediate vgps which tend to fall along american and asian longitudes roughly consistent with the sedimentary data this result is not an apparent artifact arising from the nonuniform geographic distribution of volcanic sites provided the appropriate polarity is assigned to intermediate vgps we find that icelandic vgps tend to fall along asian longitudes other patterns in the data for example latitudinal clustering of vgps or distinguishing longitudinal preferences of excursions from reversals are not resolved however it appears that in general transitional fields are nondipolar

biological markers in lacustrine chinese oil shales s u m m a r y a major objective in molecular organic geochemistry is the assessment and characterization of sedimentary depositional environments from the occurrence of specific biological marker compounds related to particular source organisms the aliphatic hydrocarbon distributions of petroleums and or sediments from chinese freshwater and hypersaline lacustrine environments are described and contrasted in the search for diagnostic features among their biological marker distributions the eocene maoming oil shale which crops out in guangdong province shows major differences in hydrocarbon composition through its stratigraphic succession these variations reflect changes in lithology and in the origins of the sedimentary organic matter as seen from petrographic examination the lower lignite and vitrinite layers contain significant contributions of biological markers from bacterial sources plus components derived from terrigenous higher plants such as c29 steroids in contrast the overlying shales show a dominance of dinoflagellate derived 4methylsteroids and culminate in an horizon with botryococcane homologues as their dominant alkanes thus the geochemical profile suggests that a swampy environment in which peats accumulated deepened to support populations of dinoflagellate and finally blooms of botryococcus green algae the aliphatic hydrocarbons of a series of sediments and petroleums from the eocene hypersaline sequence of the jianghan basin in southern hubei province shows various features that may be typical of such facies these include a dominance of even numbered n alkanes high amounts of phytane and gammacerane and an abundance of c35 hopanes similar characteristics are observed in shales from the eocene green river formation and in rozel point crude oil a petroleum thought to originate from sediments deposited under hypersaline conditions the same features also appear in a lower tertiary evaporitic mudstone from south of the renqui oil field in hebei province together with 4 methylsteranes fl carotane and 18c h oleanane a marker for terrigenous higher plants these data illustrate the potential of biological markers in the differentiation of different lacustrine environments and suggest that such characteristics may provide signatures for environmentally similar but geographically distant deposits

unusual topside ionospheric density response to the november 2003 superstorm 1 we use observations from a variety of different ground and space based instruments including ionosonde ground and space based global positioning system gps receivers magnetometers and solar wind data from the advanced composition explorer ace to examine the response of the ionospheric f2 layer height during the november 2003 superstorm we found that the topside ionosphere responded unusually to the 20 november 2003 severe storm compared to behavior observed in a number of previous storms while ground based gps receivers observed a large enhancement in dayside tec the low earth orbiting 400 km champ satellite did not show any sign of dayside tec enhancement the real time vertical density profiles constructed from ground based gps tec using a tomographic reconstruction technique clearly revealed that the ionospheric f2 layer peak height had been depressed down to lower altitudes ionospheric f layer peak height hmf2 from the nearby ionosonde stations over europe also showed that the dayside f2 layer peak height was below 350 km which is below the orbiting height of champ the vertical e b drift estimated from ground based magnetometer equatorial electrojet delta h showed strong dayside downward drifts which may be due to the ionospheric disturbance dynamo electric field produced by the large amount of energy dissipation into high latitude regions this storm demonstrates that data from leo satellites varies widely among different superstorms

an improved methodology for thellier type paleointensity determination in igneous rocks and its usefulness for verifying primary thermoremanence we propose a new methodology for thellier type paleointensity experiments in standard paleointensity experiments the blocking temperatures of most stable remanences are often not reached before thermal alteration of magnetic mineralogy begins and subsequent data have to be discarded we emphasize that when alteration begins at low temperature and continues throughout the experiment which then fails in standard analyses the resulting unblocking temperature tub spectrum of the alteration product does not necessarily overlap with the whole tub spectrum of natural remanent magnetization nrm because tub depends on physical characteristics of the new grains not the temperatures at which they were formed nrm may survive in an uncontaminated higher tub window if alteration remanence only has low tub then partial thermoremanent magnetization ptrm checks at temperature step tj 1 can be used to correct for alteration that has occurred at tj and furthermore thermal demagnetization of a full trm acquired in the laboratory at the end of the progressive thellier thellier experiment should reveal the true uncontaminated tub spectrum of the nrm in higher temperature intervals we propose a new experimental sequence which allows monitoring and correction of alteration and provides two semi independent estimates of palaeointensity in the circumstances described above we illustrate the issues involved through new experimental work on igneous rocks from a paleozoic charnockitic syenite where we unravel trm from multidomain isothermal remanence despite massive alteration during laboratory heating finally we point out the value of these experiments for verifying primary trm in igneous rocks indicating properties that distinguish trm from other remanence

absolute paleointensity and magnetomineralogical changes determinations of absolute paleointensity are often hampered by magnetomineralogical changes produced within samples of lava flows during successive heatings such changes which directly affect the capacity for a sample to acquire a partial thermoremanent magnetization ptrm are reflected by negative ptrm checks a deviation between the original ptrm and a repeated measurement after heating at a higher temperature because the deviations indicated by the ptrm checks can provide a direct estimate of the effects to the ptrms we suggest that they can be used to correct ptrms the correction method we present requires additional measurements in particular ptrm checks performed after each ptrm and specific diagrams to detect acquisition of chemical remanence performing multiple successive ptrm checks can also provide information on the blocking temperatures of the alteration product these experiments conducted on lava flows from different localities show that the magnetomineralogical changes mainly involved grains with blocking temperatures lower than the last heating step the corrections have been tested on recent and historic lava flows from several localities we have also compared results on samples from the same lava flows that were heated in air and in vacuum the mean paleointensity values were found to lie within less than 10 from the expected field intensity at each site the corrections resulted in the recovery of reliable paleointensity determinations for about twice as many specimens heated in vacuum and 65 additional data for specimens heated in air successive heatings at the same temperature in air are often accompanied by a time dependent oxidation of the natural remanent magnetization which is responsible for paleointensity values lower than the expected field a problem that is not related to the corrections we conclude that corrections can be used with fairly high confidence to the ptrms performed in vacuum and in air

high absolute paleointensity during a mid miocene excursion of the earth s magnetic field abstract a record of an excursion of the earth s magnetic field was found in a 14 3 myr old lava sequence of the shield basalts from gran canaria canary islands the thermal and alternating field demagnetization of the samples from 14 subsequent lava flows revealed mainly single component magnetizations and sometimes minor viscous overprints four consecutive flows showed intermediate paleodirections which represent an excursion of the virtual geomagnetic pole vgp from the south pole towards the equator in the central atlantic rock magnetic and microscopic analysis revealed high temperature oxidized titanomagnetites as the dominant carrier of remanence on the basis of reversibility of thermomagnetic curves and limited variation of susceptibility during thermal demagnetization we selected suitable samples for three slightly different thellier type paleointensity methods the results show a minimum in paleointensity after the directional excursion with intensity values of 9 t with the pole approaching the equator values of 27 t are reached the intensity at the beginning and at the end of the section is 20 t corresponding to a virtual dipole moment vdm of 6 1022 am2 the high intensities during the vgp excursion with a pole near the equator are explained by the same vdm

storm time dependence of equatorial disturbance dynamo zonal electric fields we use jicamarca radar observations of f region vertical plasma drifts and auroral electrojet indices during 1968 1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields these electric fields result from the dynamo action of storm time winds and or thermospheric composition changes driven by enhanced energy deposition into the high latitude ionosphere during geomagnetically active conditions the equatorial vertical drift perturbations last for periods of up to 30 hours after large increases in the high latitude currents on the average this process can be described by two basic components with time delays of about 1 12 hours and 22 28 hours between the high latitude current enhancements and the equatorial velocity perturbations our data indicate strong coupling between dynamo processes with different timescales the short term disturbance dynamo drives upward equatorial drifts eastward electric fields at night with largest amplitudes near sunrise and small downward drifts during the day these perturbation drifts are in good agreement with results from the blanc richmond disturbance dynamo theory the dynamo process with time delays of about a day drives upward drift velocities at night with largest values near midnight and downward drifts in the sunrise noon sector in this case the amplitudes of the disturbance drifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions we also present results of a new equatorial storm time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts

paleosecular variation during sequential geomagnetic reversals from hawaii abstract paleomagnetic directions measured from 175 flows in four volcanic sequences on the island of o ahu hawaii cover about 0 3 m y of geomagnetic field changes and include detailed records of the successive gilbert gauss 3 57 ma and lower mammoth reversals 3 33 ma the dominant pattern of the directional changes is the presence of large inclination variations with increasing amplitude and steep values during the transitional periods the morphology of these recurring features during different transitions is reminiscent of the characteristics of the non dipole field inferred from studies of paleosecular variation in the pacific these observations are consistent with transitional mechanisms yielding the emergence of non dipole components with characteristics similar to those during periods of stable polarity the three different records of the lower mammoth reversal show that clusters of transitional pole positions are not reproducible between parallel sections and are thus linked to local eruptions and not to long lived states of the transitional field

petroleum isotopic and biomarker composition related to source rock organic matter and depositional environment abstract a multivariate approach has been developed that separates oils derived from organic matter in nonmarine shales marine shales and marine carbonates some or all of the following analyses were completed on 43 oils from known source rocks 1 c30 sterane and monoaromatic steroid biomarker ratios and 2 stable carbon and hydrogen isotope compositions of whole oil saturates and aromatics three group discriminant analysis of the 28 oils whereall biomarker and isotopic data are available results in no misclassifications at a significance level of 99 using only carbon and hydroogen isotopic data for whole oils saturates and aromatics results in correct classifications of 82 for oils derived from marine shale organic matter and 100 for oils from the other two sources triangular plots probabilities can be used to distinguish oils derived from the three source rock organic matter end members several publications describe classifications of marine vs nonmarine oils using stable carbon isotope ratios of the whole oil or the saturate and aromatic fractions our results confirm that these methods do not completely differentiate oils by source

midlatitude tec enhancements during the october 2003 superstorm 1 we use observations from the array of north american gps receivers to examine the formation and severity of midlatitude enhancements and steep gradients in total electron content tec during the october 30 31 2003 superstorm a large 10x enhancement in dayside tec was observed over the us mainland during these events as dst decreased sharply and strong saps electric fields eroded the outer reaches of the post noon plasmasphere boundary layer pbl forming poleward streaming plumes of storm enhanced density tec increased to 250 tecu equatorward of the pbl tec gradients across the pbl over the central us exceeded 60 tecu per deg latitude while intense these features are qualitatively similar to those seen in lesser storms

millstone hill incoherent scatter f region observations during the disturbances of june 1991 the extreme geomagnetic disturbances of early june 1991 were accompanied by dramatic effects in the earth s thermosphere and ionosphere which are the subject of coordinated analysis by the coupling energetics and dynamics of atmospheric regions cedar storm study project f region observations taken at millstone hill over the interval june 5 11 using a nine position experiment allow estimation of spatial gradients in ionospheric parameters above the station from these gradients the motion term in the f region continuity equation is obtained and combined with calculations of rates of production and loss of the major ions in a semiempirical model of the f region ionosphere above millstone hill electron densities calculated from this semiempirical model using msis 86 are generally much smaller than the measurements this discrepancy could be explained by the presence of vibrationally excited n sub 2 combined with a decrease in the atomic oxygen to molecular composition ratio of approx 2 or more on the most disturbed days neutral winds calculated by using the incoherent scatter line of sight ion drifts show a strong equatorward surge during the day on june 5 and strong equatorward surges during all the disturbed nights synoptic observations taken from millstone hill by using elevation and azimuth scans duringmore the nights of june 12 13 and 14 illustrate the large scale structure of electron density and its relation to neutral winds and electric fields observed over much of eastern north america 58 refs 12 figs 1 tab less

magnetic state of 10 40 ma old ocean basalts and its implications for natural remanent magnetization abstract the natural remanent magnetization nrm of ocean basalts giving rise to the pattern of marine magnetic anomalies is known to be of comparatively low intensity for about 20 ma old oceanic crust the aim of this study is to detect possible peculiarities in the rock magnetic properties of ocean basalts of this age and to establish a link between magnetomineralogy rock magnetic parameters and the low nrm intensity ocean basalts covering ages from 0 7 to 135 ma were selected for rock magnetic experiments and their room temperature hysteresis parameters curie temperature and temperature dependence of saturation magnetization ms t was determined and complemented by reflected light microscopy the majority of samples is magnetically dominated by titanomagnetite and titanomaghemite with increasing oxidation state with age for these a strong dependence of hysteresis parameters on the age of the samples is found the samples have a minimum in saturation magnetization and a maximum in magnetic stability in the age interval ranging from approximately 10 to 40 ma coinciding with the age interval of low nrm intensity the observed change in saturation magnetization is in the same order as that for the nrm intensity a further peculiarity of the titanomaghemites from this age interval is the shape of their ms t curves which display a maximum above room temperature neel p type and sometimes a self reversal of magnetization below room temperature neel n type these special rock magnetic properties can be explained by titanomagnetite low temperature oxidation and highly oxidized titanomaghemites in the age interval 10 40 ma a corresponding measurement of the nrm at elevated temperature allows to identify a maximum in nrm intensity above room temperature for the samples in that age interval this provides evidence that the nrm is equally carried by titanomaghemites and that the low nrm intensities for about 20 ma old ocean basalts are caused consequently by the low saturation magnetization of these titanomaghemites

major unconformities termination of extension events and associated surfaces in the south china seas review and implications for tectonic development abstract the distribution of unconformities and end of cenozoic rifting events in the south china seas scs reflects both the modes of rift development and the effects of driving mechanisms continental rifting began in the eastern basins during the paleocene and propagated westwards to the vietnam basin margin in the late eocene continental breakup around 32 28 ma caused a regional reduction or cessation in extensional activity particularly affecting basins furthest from the spreading centre basins in the slope and deepwater area north of the spreading centre exhibit reduced fault activity until 21 20 ma propagation of oceanic crust westwards between 25 and 23 ma and termination of seafloor spreading sometime between 20 5 and 16 ma affected fault activity in the qiongdongnan and nam con song basins in the phu khanh basin and south in the dangerous grounds area extension continued until about 16 ma ending at the red unconformity the end of seafloor spreading around 20 5 ma reflects loss of extensional driving force as thinned continental crust entered the nw borneo subduction zone controversially a key component of the driving force maybe attributed to slab pull a transitional period of about 5 7 my between the onset of subduction of continental crust and final jamming of the subduction zone deep regional unconformity dru is inferred the last pulse of extension was focussed in the western scs and terminated around 10 5 ma detailed understanding of proto south china seas development remains uncertain and controversial

geochemical characteristics and genetic origin of crude oil in the fushan sag beibuwan basin south china sea abstract the fushan sag is an important petroleum bearing unit in the beibuwan basin south china sea however genetic relationship between oil and source rocks has not been well understood in this work 43 mudstone samples and 22 crude oil samples in the sag were collected for molecular geochemical and isotopic analyses to investigate this relationship the geochemical data shows that the mudstones in liushagang formation have poor to good oil generation potential with toc ranging from 0 45 to 2 19 wt and the kerogen is mainly type two types of crude oils were identified in this study the first type of group a oils including the subgroup a1 and subgroup a2 has the characteristics of low maturity with low saturated hydrocarbon content and lighter 13c values in the huachang uplift the source rocks for the group a oils were deposited under suboxic to oxic and freshwater environment containing more terrestrial higher plant and less angiosperm the subgroup a1 oils in els11 reservoirs are separated from subgroup a2 in the els12 reservoirs by relatively lower maturity the subgroup a1 and subgroup a2 oils are closely related to the els1 to els21 and els12 to els21 source rocks respectively while the second type of oils including group b and group c oils has higher level of maturity with higher saturated hydrocarbon content and heavier 13c values the source rocks of group b oils were deposited in a freshwater environment with lower salinity and more angiosperms and terrestrial higher plants input than those of group c oils two subgroups are divided in the group b oils of which subgroup b1 oils have higher maturity and their source rocks were deposited in lower salinity with more terrestrial higher plant input than that of subgroup b2 oils the subgroup b1 oils occurring in the els31 reservoirs from the huachang uplift are likely related to els31 source rocks while subgroup b2 oils in the els22 reservoirs from the southern slope area of the bailian subsag is linked with mixed source of els22 and els31 mudstones the group c oils are distributed in els22 and els31 reservoirs in the huachang uplift and their oil source are from els32 mudstones two petroleum plays are likely divided by the mfs in els2 based on the oil source correlation in the sag group b and group c oils belong to the lower play and group a oils only occur in the upper play the distribution and accumulation of different groups of oils are mainly controlled by the special two layered tectonostratigraphic framework and the transport ability of fault zone in the sag this study clarifies the types of oils as well as the oil source correlation and the spatial distribution of different groups of oils the results could benefit the further petroleum exploration and resource evaluation in the sag

the van zijl jurassic geomagnetic reversal revisited we have collected two new detailed records of what could be the second oldest well documented reversal the van zijl jurassic 180 ma reversal recorded in the thick basalt sequences of the karoo large igneous province in lesotho and south africa sections yielded 10 and 8 independent transitional paleomagnetic directions respectively over two continuous 130 m and 160 m sequences the corresponding vgp reversing paths share a number of consistent features and are integrated with a third record at bushmen s pass from prevot et al 2003 to yield a single reversal path with 1 a large directional jump with no transitional poles between 45 s and 45 n in the first main phase of the reversal 2 a large elongated loop multiple hairpin to the se with poles going down to 20 latitudes in the second phase of the reversal and 3 a rebound before finally settling in normal polarity we have measured relative paleo intensities on a set of carefully selected samples intensity was low prior to the directional changes and recovery to the following normal polarity was progressive transitional intensity is 80 to 90 lower than full polarity values there is no significant increase in intensity at the time of transitional directional clusters our results are consistent with a weak non dipolar reversing field with faster and larger directional secular variation as the equator is crossed by vgps they tend to vindicate the notion of a short duration of the directional reversal though one cannot draw global conclusions from a record limited to essentially a single location

correlation of the permian triassic ore bearing intrusions of the norilsk region with the volcanic sequence of the siberian traps based on the paleomagnetic data

detecting multidomain magnetic grains in thellier palaeointensity experiments the thellier technique is the most commonly used method for absolute palaeointensity studies it is based on thellier s laws stating that partial thermoremanent magnetisations ptrms are independent and additive which however only are true for non interacting single domain sd grains for multidomain md grains individual ptrms are not independent and thellier palaeointensity experiments on rocks with a significant proportion of md grains may therefore lead to erroneous palaeofield estimates by introducing a ptrm tail check in the coe version of the thellier technique j geophys res 72 1967 3247 we present a simple method to detect and discard such rocks the usefulness of the ptrm tail check is exemplified by thellier palaeointensity experiments performed on two palaeomagnetic sample collections with different magnetomineralogy miocene baked sediments from french massif central are shown to be ideal for thellier studies with the remanent magnetisation residing in thermally stable sd grains for palaeocene eocene basaltic lavas from faeroe islands 64 of otherwise acceptable palaeointensity estimates are discarded due to the failure of ptrm tail checks indicating the presence of significant concentrations of md grains 2001 elsevier science b v all rights reserved

oil source and charge in the wuerxun depression hailar basin northeast china a chemometric study abstract one hundred fifty four samples collected from the wuerxun depression hailar basin northeast china were analyzed using gc ms the k1n formation including k1n2 and k1n1 members consists mainly of argillaceous rock with relatively abundant organic matter and is considered to be the best source rock in the study area whereas the k1t formation and k1d1 member damoguaihe formation provide a limited contribution to the wuerxun oils chemometric methods i e principal component analysis pca and multidimensional scaling mds were used for oil oil and oil source rock correlations in this study based on pca and geological evidence the oils from northern wuerxun originated primarily from source rocks of the k1n1 member that were charged ca 100 ma whereas those in the southern wuerxun form separate genetic groups i and ii when combined with trend surface analysis the mds technique also revealed variations in the depositional conditions and the maturity of the source rocks and oils group i oils which have relatively higher maturity are characterized by relatively high saturate aromatic hydrocarbon ratios high pr ph ratios 1 high ts ts tm ratios a slight predominance of c29 regular steranes and more positive 13c values of saturated and aromatic hydrocarbon fractions whereas the lower maturity group ii oils have relatively low saturate aromatic hydrocarbon ratios low pr ph ratios

microwave palaeointensities from holocene age hawaiian lavas investigation of magnetic properties and comparison with thermal palaeointensities abstract sixteen c 14 dated hawaiian surface lava flows spanning 0 4 5 ka have been investigated using the microwave perpendicular applied field palaeointensity technique and classical thermal thellier thellier palaeointensity technique in parallel the overall microwave experimental success rate is 63 compared to 59 in the thermal experiments nineteen percent of the microwave results are deemed to be first class compared to 52 of the thermal results high palaeointensities and a large amount of within flow variation are seen in the microwave results with reliable palaeointensity estimates ranging from 25 10 to 82 94 t these variations do not appear to be systematically related to variations in rock magnetic properties such as mineralogy grain size texture or oxidation state the flow means from the microwave and thermal studies agree for 9 of the 13 flows that can be directly compared and the average difference between the two techniques is not significantly different from zero neither experimental technique produces mean palaeointensities systematically lower or more precise than the other suggesting that the differences seen are a reflection of natural within flow variation rather than experimental technique

geochemical characteristics palaeoenvironment and formation model of eocene organic rich shales in the beibuwan basin south china sea abstract lacustrine organic rich shales in the eocene are the most important source rock in the beibuwan basin palynological petrographical and geochemical data were applied to define their palaeoenvironment formation and petroleum potential toc values range from 2 84 to 14 77 and the kerogens of these dark gray or brown shales with numerous lamalginites can be classified as oil prone type i and type ii1 biomarkers are characterized by a high abundance of c30 4 methylsteranes a low content of oleanane and diterpanes relatively abundant pentacyclic terpanes which indicate that the organic matter in the shales is typically algal and microbial origin abundance of amorphous organic matter the presence of low level gammacerane small amounts of pyrite pr ph ratios of 1 38 2 42 and v v ni ratios of 0 74 0 84 suggest that the organic rich shales were formed in a less oxic to anoxic stratified fresh brackish lake environment with a relatively low sedimentation rate for this starved lake basin the bloom and death of algae in nutrient rich surface water supplied a large amount of organic matter to the lacustrine sediments the oxygen depleted bottom waters of the palaeo lakes favored the accumulation and preservation of sedimentary organic matter resulting in the formation of the organic rich shale a high quality source rock future exploration or assessment of the petroleum potential of the basin could be assisted by considering the proposed formation model of the organic rich shales and their distribution relative to potential traps

topside ionospheric irregularities as seen from multisatellite observations we use in situ data from champ and dmsp satellites along with data of gps receiver onboard champ satellite and ground based gps receivers to study the occurrence and global distribution of ionospheric irregularities during the main phase of the geomagnetic storm of 29 31 august 2004 minimum dst excursion of a128 nt using the champ gps measurements we created maps of gps phase fluctuation activity and found two specific zones of the most intense irregularities 1 the region of the auroral oval at high latitudes of both hemispheres and 2 the low latitudes equatorial region between africa and south america at high latitudes the topside ionospheric irregularities appeared to be more intensive in the southern hemisphere which is most likely due to seasonal variations in the interhemispheric field aligned currents system an analysis of multi instrumental observations reveals reinforcement of the equatorial ionization anomaly after sunset in atlantic sector on 30 august and formation of the significant plasma depletions and irregularities over a large longitudinal range equatorial irregularities were also found in the morning sector at the recovery phase of the storm in addition to low earth orbit leo gps measurements we analyze the leo in situ measurements and we show that these two techniques cannot be interchangeable in all cases because of the altitudinal extent of plasma irregularities overall we demonstrate that the leo gps technique can serve a useful tool for detection of the topside ionospheric irregularities during space weather events and may essentially contribute to other methods based on various instruments

oil families and their source rocks in the weixinan sub basin beibuwan basin south china sea abstract thirty one crude oils and 15 source rocks were selected for molecular geochemical and isotopic analyses in order to establish the genetic relationships between discovered oils and petroleum source rocks in the weixinan sub basin beibuwan basin south china sea three groups of oils were recognized group i oils are only found in the upper section of the liusagang formation with a moderate abundance of c 30 4 methylsteranes low oleanane contents and lighter 13 c values showing a close relation to the shale occurring in the upper section of the liusagang formation group ii is represented by the majority of the discoveries and is distributed in multi sets of reservoirs having different ages the oils are characterized by a high abundance of c 30 4 methylsteranes low to moderate abundance of oleanane and heavy 13 c values and shows a good correlation with the lacustrine shale and oil shale in the middle section of the liusagang formation group iii oils occurred in the lower section of the liusagang formation the oils have a lower concentration of c 30 4 methylsteranes relatively high abundance of oleananes and their 13 c values are intermediate oils of this group correlated well with the shallow lake delta mudstone of the lower section of liusagang formation these oil source genetic relationships suggest a strong source facies control on the geographic distribution of oil groups within the weixinan sub basin the geochemical data indicate shale in the middle section of the liusagang formation has an excellent oil generation potential and the lower and upper sections contain dark shale and mudstone with good to fair oil potential future exploration or assessment of petroleum potential of the sub basin could be improved by considering the proposed genetic relationship between the oil types and source rocks as well as their distribution

geochemistry grouping and origins of crude oils in the western pearl river mouth basin offshore south china sea abstract thirty seven crude oils and 20 source rocks were selected for detailed molecular geochemical and isotopic analyses in order to establish the genetic relationships between the discovered oils and various petroleum source facies in the western pearl river basin offshore south china sea four groups of oils were identified the group i oils distributed in the southwestern wc19 1 field of wenchang b sag are characterized by high abundance of 4 methyl steranes relative to regular steranes low abundance of bicadinanes and high 13 c values showing good correlation with the medium deep lacustrine source facies in the wenchang formation the group ii oils represent the majority of the discovered oil reserves in the study area including those from the qionghai uplift and the northeast block of the wc19 1 oil field these oils have moderate concentrations of c 30 4 methylsteranes abundant bicadinanes and low 13 c values and correlate well with the shallow lake source facies of the wenchang formation in the wenchang b and a sags the group iii oils found in the wenchang a sag and surrounding areas are devoid of c 30 4 methylsteranes with abundant bicadinanes and similar 13 c values to those of the group ii oils these characteristics show close affinity with the coal bearing sequence in the enping formation thus suggesting a coaly source for these oils the group iv oils found only in the wc8 3 field display intermediate chemical compositions between the group ii and group iii oils most likely from mixed sources in the wenchang a sag these oil source genetic relationships suggest dominantly short distance oil migration and thus strong source facies controls on the geographic distribution of oil and gas fields within the western pearl river mouth basin

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

impact of marine incursions on lacustrine source rocks organic matter quantity quality and kinetics in the paleocene south yellow sea basin offshore eastern china abstract the impact of marine incursions during transgression on the quantity and quality of organic matter in lacustrine source rocks is critical to understanding their source rock properties and therefore on their hydrocarbon generation potential but is also challenging and controversial here we examine this issue based on a case study in the south yellow sea basin sysb offshore eastern china addressing organic matter om quantity quality and petroleum generation kinetics a total of 139 lacustrine source rock samples was collected from the fourth member of the paleocene funing formation e1f4 in the sysb and investigated for organic petrographic and geochemical characteristics the samples are immature to early oil window mature and the om in all samples is dominated by terrigenous material as shown by the organic petrography relatively low hydrogen indices and biomarker distributions the sediments are classified as inert to gas prone however the presence of marine fossils red and brown algae coccolithophores and probably neomonoceratinabullata and the biomarker results suggest that marine incursions occurred during the deposition of the lower unit of the e1f4 e1f4l the samples from this unit display higher hi values and more depleted 13corg ratios but lower toc and s1 s2 contents than the upper unit of the e1f4 e1f4u source rocks without marine influence this suggests that marine incursions primarily improved the quality rather than quantity of organic matter bulk kinetics indicated that marine incursions also led to a more homogenous om and compositional kinetics and phase properties suggest that black oil is generated throughout the process of kerogen conversion thus our data suggest that marine incursions had a positive effect on the om quality and oil generation potential of these lacustrine source rocks therefore the impact of marine incursions should be fully considered during source rock evaluation of coastal lacustrine basins especially during high sea level stages in addition the greatest hydrocarbon exploration potential is observed in the south 4th sag of the southern depression and thus this study provides valuable data for shaping regional exploration strategy in the sysb

synchrony and causal relations between permian triassic boundary crises and siberian flood volcanism the permian triassic boundary records the most severe mass extinctions in earth9s history siberian flood volcanism the most profuse known such subaerial event produced 2 million to 3 million cubic kilometers of volcanic ejecta in approximately 1 million years or less analysis of 40 ar 39 ar data from two tuffs in southern china yielded a date of 250 0 0 2 million years ago for the permian triassic boundary which is comparable to the inception of main stage siberian flood volcanism at 250 0 0 3 million years ago volcanogenic sulfate aerosols and the dynamic effects of the siberian plume likely contributed to environmental extrema that led to the mass extinctions

equatorial disturbance dynamo electric fields f region vertical drift data from jicamarca peru show that equatorial east west electric fields are sometimes perturbed 16 24 hours after the onset of geomagnetic storms these disturbance dynamo electric fields which must be caused primarily by the action of neutral winds at low and middle latitudes decrease and sometimes even reverse the quiet time electric field pattern during both daytime and nighttime the long delay excludes the possibility that gravity waves are responsible and suggests that the thermospheric circulation is disturbed the data also show that after some storms there are no such delayed disturbances a fact which may be due to the longitudinal structure of the disturbances at high latitudes and or that only very strong storms can produce major thermospheric perturbations that extend to middle and low latitudes

ground observation and amie tiegcm modeling of a storm time traveling ionospheric disturbance 1 this paper reports the first comparison between comprehensive observations of equatorward moving traveling ionospheric disturbance at midlatitudes and thermospheric general circulation model with high latitude energy input based on data assimilation a prominent traveling ionospheric disturbance tid was observed during the major magnetic storm of 31 march 2001 the tid propagated from north to south over japan with phase speeds of 370 640 m s the assimilative mapping of ionospheric electrodynamics amie technique was used as input to the thermosphere ionosphere electrodynamics general circulation model tiegcm to investigate generation and propagation of the observed tid in the model two joule heating enhancements in the high latitude dayside sector produced two distinct traveling atmospheric waves tads which propagated to japan in the midnight sector as enhancements in thermospheric temperature and southward wind speed the phase speed of the tads was much faster 1100 m s in the model probably due to the overestimation of joule heating in the model the second tad corresponds to the observed prominent tid while signatures of the first tad were also seen in the observed ionosonde data the observed tid was characterized by a decrease in southward wind speed causing a significant f layer height decrease and a temporal enhancement of f layer peak density these characteristics were reproduced by the model as a rarefaction of the second tad the temporal enhancement of f layer peak density was because of the vertical shear of meridional wind the absolute value of f layer electron density in the model was several factors smaller than that observed probably because of the underestimation of the supply of o ions from the plasmasphere

ionospheric signatures of plasmaspheric tails 1 we make direct comparisons between gps maps of total electron content tec over the north american continent millstone hill radar observations of storm enhanced density and low and high altitude satellite measurements of the perturbation of the outer plasmasphere during the march 31 2001 geomagnetic storm we find that storm enhanced density sed and plumes of greatly elevated tec are associated with the erosion of the outer plasmasphere by strong sub auroral polarization electric fields the sed tec plumes identified at low altitude map closely onto the magnetospheric determination of the boundaries of the plasmapause and plasmaspheric tail determined by euv imaging from the image spacecraft characteristics of the sed tec plumes tails for the march 31 2001 event are tec 100 tecu f region sunward velocity 1000 m s sunward flux 5 1024 ions s 1 total transport to dayside magnetopause merging region 3 hr event 5 1028 ions

the c27n c26r geomagnetic polarity reversal recorded in the west greenland flood basalt province how complex is the transitional field 1 we present a paleomagnetic record of the c27n c26r 60 9 ma geomagnetic polarity reversal gpr sampled in two separate lava sequences in the vaigat formation west greenland flood basalt province the two profiles distanced 16 km apart consist of 45 and 35 sampled lava flows of which 31 and 23 respectively record transitional field directions a prominent feature of each profile is the presence of successive flows with similar paleomagnetic directions which based on geological geochemical and paleomagnetic evidences are interpreted to represent flow fields i e lavas erupted in a short period of time rather than periods when the geomagnetic field stood still multimodel photogrammetry shows that the typical flow length of vaigat formation picritic lavas is 2 km which explains why flow to flow correlation of paleomagnetic directions between the two profiles 16 km apart is not possible the two profiles therefore record different and independent time series of the same gpr allowing us to cast light on some of the questions that have arisen from single records particularly noteworthy is the fact that the two high resolution paleomagnetic records share no general trends clearly indicating that the c27n c26r transitional field was more complex and faster changing than can be resolved by either record in addition we obtained stable polarity paleomagnetic data from both pretransitional c27n and posttransitional c26r yielding a paleomagnetic pole latitude 64 8 n longitude 141 5 e n 14 k 19 8 a95 9 2 that passes reversal test

dynamical similarity of geomagnetic field reversals volcanic records of the reversals of the geomagnetic field can be well matched under the assumption of a common reversal duration and imply that the reversal process comprises three phases a precursor a fast polarity switch and a rebound the properties of which have remained unchanged for about 180 million years the geomagnetic variations that prevail during magnetic field reversals convey important information on the nature of the geodynamo that drives earth s magnetic field in this paper jean pierre valet and co authors show that the ten most detailed volcanic records of geomagnetic reversals have a common duration as well as common dynamical characteristics they propose that the reversing process has remained the same for at least the past 180 million years characterized by three phases a precursor event a 180o polarity switch and then a rebound no consensus has been reached so far on the properties of the geomagnetic field during reversals or on the main features that might reveal its dynamics a main characteristic of the reversing field is a large decrease in the axial dipole and the dominant role of non dipole components1 2 3 other features strongly depend on whether they are derived from sedimentary or volcanic records only thermal remanent magnetization of lava flows can capture faithful records of a rapidly varying non dipole field but because of episodic volcanic activity sequences of overlying flows yield incomplete records here we show that the ten most detailed volcanic records of reversals can be matched in a very satisfactory way under the assumption of a common duration revealing common dynamical characteristics we infer that the reversal process has remained unchanged with the same time constants and durations at least since 180 million years ago we propose that the reversing field is characterized by three successive phases a precursory event a 180 polarity switch and a rebound the first and third phases reflect the emergence of the non dipole field with large amplitude secular variation they are rarely both recorded at the same site owing to the rapidly changing field geometry and last for less than 2 500 years the actual transit between the two polarities does not last longer than 1 000 years and might therefore result from mechanisms other than those governing normal secular variation such changes are too brief to be accurately recorded by most sediments

late devonian palaeomagnetism of the north tien shan kyrgyzstan can secular variation vary on a short timescale summary we studied more than 80 lava flows from a 600 m thick pile of upper devonian frasnian basalts and andesites of the aral formation in the north tien shan kyrgyzstan central asia with the aid of stepwise thermal demagnetization a high temperature dual polarity component was reliably isolated from most flows the primary origin of the high temperature component is demonstrated by positive reversal conglomerate and fold tests the most prominent and intriguing feature of this late devonian data set involves a clear distinction in angular dispersion between the lower and upper parts of the studied section a rather low concentration parameter k 13 and several directional anomalies characterize the lower section in contrast a much better grouping k 46 and a lack of directional outliers is observed for the dual polarity vectors from the upper flow sequence of the formation we analysed different mechanisms to account for this directional pattern and found that it is possible in just two ways one is to assume that secular variation sv in the upper sequence is strongly underrepresented and it is a coincidence that the mean directions of both polarities are statistically antipodal and the corresponding concentration parameters are statistically equal the other explanation is to hypothesize that the magnitude of sv can vary several fold at the same palaeolatitude and over time intervals estimated as 10 5 10 6 yr this is in sharp contrast with other models of sv where this magnitude has been assumed to be rather time independent for a givenlatitude ourhypothesisaccountsfortheobservedirregularitiesinpalaeomagneticdata but makes attempts to establish a correlation between sv and other parameters geographic latitude reversal frequency age etc more difficult we are aware however that more data are needed to refute or confirm it

siberian traps volcaniclastic rocks and the role of magma water interactions the siberian traps are one of the largest known continental flood basalt provinces and may be causally related to the end permian mass extinction in some areas a large fraction of the siberian traps volcanic sequence consists of mafic volcaniclastic rocks here we synthesize paleomagnetic petrographic and field data to assess the likely origins of these volcaniclastic rocks and their significance for the overall environmental impact of the eruptions we argue that magma water interactions including both lava water interactions and phreatomagmatic explosions in vents were important components of siberian traps magmatism phreatomagmatic episodes may have generated tall water rich eruption columns simultaneously promoting removal of highly soluble volcanic gases such as hcl and potentially delivering additional sulfur to the upper atmosphere

the role of the earth s mantle in controlling the frequency of geomagnetic reversals a series of computer simulations of the earth s dynamo illustrates how the thermal structure of the lowermost mantle might affect convection and magnetic field generation in the fluid core eight different patterns of heat flux from the core to the mantle are imposed over the core mantle boundary spontaneous magnetic dipole reversals and excursions occur in seven of these cases although sometimes the field only reverses in the outer part of the core and then quickly reverses back the results suggest correlations among the frequency of reversals the duration over which the reversals occur the magnetic field intensity and the secular variation the case with uniform heat flux at the core mantle boundary appears most earth like this result suggests that variations in heat flux at the core mantle boundary of the earth are smaller than previously thought possibly because seismic velocity anomalies in the lowermost mantle might have more of a compositional rather than thermal origin or because of enhanced heat flux in the mantle s zones of ultra low seismic velocity