study of the effect of 17 18 march 2015 geomagnetic storm on the indian longitudes using gps and c nofs the largest geomagnetic storm in solar cycle 24 occurred during march 17 18 2015 where the main phase of the storm commenced from 07 00 ut of march 17 2015 and reached the dst negative minimum at 22 00 ut the present paper reports observations of tec amplitude and phase scintillations from different gps stations of india during the storm of march 17 and highlights its effects on gps it also presents the global esf occurrence during the storm using total ion density drift measurements from c nofs satellite tec enhancements were noted from stations along 77oe meridian around 10 00 ut on march 17 compared to march 16 and 18 indicating positive storm effects arising out of equatorward neutral wind in the local morning noon sector of the main phase intense scintillation observations from calcutta were most extensive during 15 00 16 00 ut march 17 and the receiver recorded a longitude deviation of 5 2 m during this time cycle slips of the order of 8 s could be observed during periods of intense phase scintillations on the same night intense scintillation observation from palampur is an exceptional phenomenon attributed to the dramatic enhancement of the electric field due to ppef leading to a very high upward ion velocity over the magnetic equator as recorded by c nofs the total ion density measured globally by c nofs reveals two distinct longitude regions of esf occurrence during the storm i east pacific sector and ii indian longitude during the storm the time and longitude of esf occurrence could be predicted using the time of southward turning of imf bz

the paleohydrology of lower cretaceous seasonal wetlands isle of wight southern england abstract the floodplain deposits of the wealden group lower cretaceous of the isle of wight southern england were formed in a seasonal wetland setting a type of environment widespread today along higher order tropical and subtropical river systems but rarely identified in the geological record the unit consists of four main lithofacies sheet sandstones with dinosaur footprint casts green gray mudstones with vertebrate remains abundant lignite pyrite and siderite spectacularly color mottled mudstones with goethite and locally pseudo anticlines and red mudstones with pseudo anticlines hematite and carbonate nodules the sheet sandstones are interpreted as crevasse deposits the green gray mudstones were deposited in shallow ponds on the floodplain which acted as sinks for debris released by local floods following wildfires the mottled mudstones represent surface water gley soils formed in seasonally waterlogged areas and the red mudstones resemble present day vertisols that formed on topographically elevated areas only intermittently flooded these mudstones show vertical transitions from one to another and although they could be interpreted as components of simple catenas the absence of associated facies changes implies that topographic differences were not the only control it is proposed that these three mudstone types formed as seasonal wetland catenas in which differences in soil drainage conditions resulted from variations in the flooding hydroperiod affecting areas with minor relief differences rather than drainage variability simply reflecting static topographic differences such seasonal wetland systems are rarely documented in the stratigraphic record despite being a widespread environment in present day tropical regions and the wealden deposits are used to identify criteria for the recognition of this important environment in the rock record these southern english wetlands are compared with other lower cretaceous wetlands from northern spain enabling hydrological factors which controlled deposition to be recognized

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

from quantitative 3d seismic stratigraphy to sequence stratigraphy insights into the vertical and lateral variability of shelf margin depositional systems at different stratigraphic orders abstract a major challenge in sequence stratigraphy is objectively identifying stratigraphic surfaces and sequences across multiple scales of observation identification is commonly dependent on the resolution of the data used i e seismic vs well data its dimension i e 1d vs 2d vs 3d or the criteria chosen to select sequence boundaries through shelf edge trajectory analysis the clinothem i e highest order seismic sequence identified on seismic data can constitute the elementary building block of an observation based and data driven quantitative workflow to develop sequence stratigraphic frameworks across different orders and ranks of hierarchy here we use high quality 3d seismic data to interpret a late tithonian early cretaceous shelf margin the lower barrow group lbg developed in the northern carnarvon basin on the north west shelf of australia based on full volume seismic interpretation techniques that integrate the 3d variability of the data when identifying seismic unconformities a high resolution seismic stratigraphic framework was built 73 interpreted clinothems with an average time duration of 63 000 yrs the computation of high frequency shelf edge trajectory angle tse curves on selected seismic cross sections is used to objectively pick sequence stratigraphic surfaces based on the accommodation succession method thereby highlighting small changes in trajectory and proposing a method reproducible by interpreters based on the same quantitative data within the d lobispinosum interval 142 3 140 9 ma the definition of stratigraphic sequences and composite stratigraphic sequences through this workflow is used to discriminate the controls at high and low temporal frequency on the vertical and lateral variability which is here quantified of this shelf slope basin system the results show that the high frequency interplay between short term glacio eustasy i e milankovitch eccentricity cycles of 100 000 yrs and sediment supply locus of fluvial input along the margin impacted the three dimensional stratigraphic architecture of the lbg in contrast tectonic subsidence had a significant impact on the stratigraphic architecture of the lbg within the main depocentre at lower temporal frequency by overprinting the eustatic signal and accelerating decelerating the rates of accommodation creation however identification of long term glacio eustatic milankovitch cycles 400 000 yrs outside the main depocentre where the rates of accommodation creation due to rift related subsidence are moderate also suggests low frequency eustatic control therefore the vertical and lateral variability of the lbg results from variations in sediment supply and subsidence regime under local i e process regime currents regional i e tectonics and global i e eustasy climate forcing parameters interplaying across timescales in contrast to standard sequence stratigraphic workflows that are based on model dependent choices to select sequence boundaries quantitative 3d seismic stratigraphy constitutes an improved method to interpret 3d seismic data in shelf margin depositional systems within a sequence stratigraphic framework which provides an observation based and model independent tool allowing the definition of stratigraphic sequences with results that are reproducible across multiple stratigraphers this work highlights the need for developing new sequence stratigraphic tools and methods that integrate the 4d variability of depositional systems and moves beyond the two dimensionality inherent to current sequence stratigraphic methods quantitative 3d seismic stratigraphy represents a first step towards the creation of 3d sequence stratigraphic workflows that could improve the prediction of stratigraphic patterns and facies relationships source reservoir seal distribution across shelf margins

palaeoenvironment of the eocene eckfeld maar lake germany implications from geochemical analysis of the oil shale sequence abstract drill core samples from the depth interval between 19 4 and 32 0 m of the laminated central lake facies of the eocene eckfeld maar were investigated for biomarker and stable isotope composition bulk organic geochemical parameters c n hi and the molecular composition of the soluble organic matter indicate a dominance of particulate organic matter from land plants and microbially derived lipids in the lower part of the sedimentary succession an angiosperm dominated vegetation is indicated from the terpenoid biomarker composition abundant 4 methylsteroids in the 25 6 30 8 m section of the oil shale sequence reflect a contribution of algal derived biomass samples with high concentrations of methylsteroids are characterized by low amounts of triterpenoids related to the arborane skeleton and vice versa this pattern is interpreted as reflecting differences in autochthonous organic matter production vs microbial activity in the lowermost section 32 0 30 6 m a trend towards heavier 18 o and 13 c values indicates the evolution of permanently meromictic conditions in the lake and an increase in methanogenesis high 13 c values of siderites 10 throughout most of the sequence are consistent with permanently anoxic conditions at the sediment water interface the lighter 18 o values of siderites from turbidites relative to siderites from biogenic laminites are postulated to have been caused by temporary phases of increased precipitation followed by landslides and improved circulation within the lake depletion of the organic matter in 13 c average 13 c 29 4 in comparison with the fossil wood ranging from 23 1 to 26 6 is explained by the dominance of waxy lipid rich land plant material e g leaf waxes resins bark over wood supplied to the lake carbon cycling during anoxic decomposition of organic matter is assumed to further affect the 13 c values through the activity of anaerobic e g methanogenic bacteria resulting in a depletion of the biomass in 13 c the overall trend in the isotopic composition of organic carbon towards heavier values in the depth interval between 26 0 and 3 2 m is accompanied by decreasing c n ratios indicating an increase in aquatic organic matter production the geochemistry of the oil shale succession points towards a highly productive eutrophic ecosystem with intense microbial activity under meromictic conditions in the maar lake beside the high input of land plants to the biomass major contributions from bacteria and phytoplankton are indicated by the biomarker composition

constraints on palaeoenvironments in the lower cretaceous wealden of southern england from the geochemistry of sphaerosiderites abstract sphaerosiderites are millimetre scale concretions of feco 3 that form predominantly in waterlogged environments and are of use in palaeoenvironmental and palaeohydrological studies we present petrographic elemental and stable isotopic 13 c 18 o data from sphaerosiderites collected from the lower cretaceous wealden sediments of southern england the sphaerosiderites are composed of very pure feco 3 with only small amounts of ca mg and mn present suggesting that they are well preserved and were precipitated from fresh groundwater 13 c values display a relatively large range from about 5 to 30 vpdb in contrast 18 o values are relatively invariant 1 0 83 with an average of 3 01 vpdb the relationship between carbon and oxygen suggests that the sphaerosiderites faithfully record palaeo groundwater 18 o likely 18 o values for groundwater were calculated using a published experimentally derived siderite water fractionation equation and plausible assumed values for palaeotemperature the average estimate was 4 9 smow the wealden sphaerosiderite oxygen isotope values are comparable with other early cretaceous data from similar palaeolatitudes but lower than estimated holocene values for equivalent latitudes this observation may indicate greater rainfall at 30 n during the cretaceous relative to the holocene and also suggests relative stability of palaeoclimatic conditions during the early cretaceous at this palaeolatitude

the barremian aptian arid phase in western europe abstract evidence is presented from nine areas in western europe speeton yorkshire southern north sea channel and weald basins southern england jeanne d arc lusitanian and aquitanian basins of the north atlantic continental margins lower saxony basin north germany the paris basin and southern france for a phase of aridity which began during the hauterivian middle barremian and continued to dominate the climate of the region until the mid aptian although conditions during this period were not uniformly dry throughout criteria for recognising arid environments include the occurrence of evaporites abundances of carbonate rich sediments red beds firmgrounds carbonate nodules and pyrite concretions depletion of kaolinite spore assemblages of limited morphological diversity and the presence of numerous coniferalean and cheirolepidiacean pollen grains the change from generally humid to dry climates during the barremian is thought to have been linked to a lowering of sea level the arid phase clearly falls within the time span of the first cretaceous oceanic anoxic event

an early cretaceous lacustrine record organic matter and organic carbon isotopes at bernissart mons basin belgium abstract the early cretaceous bernissart lake deposits mons basin belgium constitute an important historical site in the field of palaeontology in this study we focus on the organic matter om content of the 50 m long borehole core ber 3 drilled at bernissart organic data rock eval palynofacies c n ratios and carbon isotope measurements on bulk om and selected isolated wood fragments were collected the om distribution exhibits two total organic carbon toc cycles 12 m and 38 m thick respectively that are stacked in a lower frequency cyclic pattern a general increase of in situ aquatic production and preservation of om through time is evidenced within the freshwater masses a spectral analysis of a high resolution gamma ray record demonstrates that the sedimentation was controlled by orbitally induced climatic changes precession obliquity and short and long term eccentricity cycles are recognized the 12 m thick and the 38 m thick toc cycles fit well with a 100 kyr short term and a 400 kyr long term eccentricity cycle respectively long term organic fluctuations are interpreted as resulting from orbitally induced fluctuating lake levels through time carbon isotope evolution of bulk om is thought to reflect firstly two local patterns of sedimentation 1 the changing contribution of in situ amorphous organic matter versus terrestrial om and 2 the possible influence of enhanced productivity the negative 13 c wood trend recorded at bernissart seems equivalent to published coeval 13 c wood and 13 c carb in the upper barremian to lower aptian this trend noted at bernissart is thus regarded as reflecting changes of the carbon isotope ratios of atmospheric co 2 previous presented palynological data suggest a middle barremian to lowermost aptian stratigraphic range for the succession at bernissart according to this new dataset we refine the age assignment for bernissart the duration of deposition is now estimated to range between 0 55 and 2 2 myr in the upper barremian to lowermost aptian

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

organofacies and paleoenvironment of lower carboniferous mudstones dishuiquan formation in eastern junggar nw china abstract the sedimentary rocks of the dishuiquan formation represent an important potential source for volcanic rock reservoirs and record the transition of the depositional environment from marine to terrestrial during paleo junggar oceanic subduction the source rock potential and paleoenvironment of mudstones from dishuiquan formation in eastern junggar were determined by organic petrography rock eval molecular and stable carbon 13 c analyses toc s 2 and hydrogen index hi values suggest a fair to good organic richness in mudstone samples from the c 2 well moreover an early mature to mature state for all the samples is inferred based on the rock eval and biomarker parameters the maceral composition molecular geochemistry and carbon isotopic results for kerogen reveal that all the mudstone samples are characterized by a mixed organic matter assemblage types ii iii with relatively high percentages of terrigenous organic matter the low to intermediate values of pr ph and the high abundances of carotene and gammacerane indicate the presence of a dysoxic reducing high salinity sedimentary environment during the deposition of the dishuiquan formation numerous parameters derived from the organic geochemical analyses indicate that the terrigenous organic matter increased with decreasing salinity and oxidation in the sedimentary environment this study concludes that a warm wet climate provided a continuous fluvial input of terrigenous plant debris and fresh water the organic geochemical data combined with the tectonic setting reveal a restricted semi closed marine depositional environment during the deposition of the dishuiquan formation in the early carboniferous

characteristics of penetration electric fields to the equatorial ionosphere during southward and northward imf turnings 1 the signatures of abrupt turnings of the vertical component of the interplanetary magnetic field imf bz can be seen at equatorial latitudes through the prompt transmission of high latitude electric fields to the lower latitudes called as prompt penetration electric field ppe the present work studies the signatures of ppe in daytime equatorial electrojet eej index derived in the indian sector during 2001 2005 the signatures are observed in polar pcn index and equatorial eej index ionosphere almost instantaneously 1 min the communication time of 12 6 min is observed between bow shock nose and the equatorial ionosphere and it is found to have inverse relationship with radial component of solar wind velocity during southward and northward bz turnings which might indicate magnetosphere crossing time scale by solar wind ionospheric reconfiguration time during southward turnings shows inverse relationship with solar wind flow in contrast to northward turnings with no relationship indicating differences in underlying physical mechanisms during both turnings we observe no local time dependence within 06 18 h in conductivity corrected eej signatures associated with bz turnings regression analysis between conductivity corrected eej and interplanetary electric field shows higher efficiency during northward turnings however further analysis investigating the effect of actual orientation of bz indicates that the magnitude of northward bz does not have influence on the ionospheric signatures it is noticed that the response signatures are mainly controlled by the magnitudes of southward bz thus the present study signifies the role of inner magnetospheric shielding electric field in addition to ceasing of convection during northward turnings

comparison of stable carbon isotope ratios in the whole wood cellulose and lignin of oak tree rings abstract the stable carbon isotope ratios 13c of whole wood cellulose and acid insoluble lignin from annual latewood increments of quercus robur l from modern and sub fossil wood were measured and their potential use as palaeoenvironmental indicators examined the resulting time series demonstrate a very high degree of coherence with 13c of cellulose isotopically enriched by approximately 3 compared to 13c of lignin the 13c values of all three components are influenced by the climate of july and august modern whole wood retains the strongest climate signal perhaps because its composition is closest to that of leaf sugars in sub fossil wood there is no evidence that differential decay leads to fractionation of carbon within either cellulose or lignin but differential decay can alter the cellulose to lignin ratio

middle and low latitude ionosphere response to 2015 st patrick s day geomagnetic storm this paper presents a study of the st patrick s day storm of 2015 with its ionospheric response at middle and low latitudes the effects of the storm in each longitudinal sector asian african american and pacific are characterized using global and regional electron content at the beginning of the storm one or two ionospheric positive storm effects are observed depending on the longitudinal zones after the main phase of the storm a strong decrease in ionization is observed at all longitudes lasting several days the american region exhibits the most remarkable increase in vertical total electron content vtec while in the asian sector the largest decrease in vtec is observed at low latitudes using spectral analysis we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field ppef and of the disturbance dynamo electric field ddef on the basis of ground magnetic data concerning the ppef earth s magnetic field oscillations occur simultaneously in the asian african and american sectors during southward magnetization of the b z component of the interplanetary magnetic field concerning the ddef diurnal magnetic oscillations in the horizontal component h of the earth s magnetic field exhibit a behavior that is opposed to the regular one these diurnal oscillations are recognized to last several days in all longitudinal sectors the observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models

controls on organic matter enrichment in source rocks of the shahejie formation in the southwestern bozhong sag bohai bay basin china abstract with the discovery of the bozhong 19 6 large gas field in the bohai bay basin the study of lacustrine source rocks in the southwestern bozhong sag has garnered new interest in this paper 107 source rock samples of the paleogene shahejie formation es from the southwestern bozhong sag were analyzed with organic and inorganic methods and compared with other sags in the bohai bay basin to reveal the depositional environment and controlling factors of organic matter enrichment during the deposition of the es the formation of source rocks average total organic content 2 76 was subject to a combination of high organic productivity and enhanced organic preservation also this was reflected by the existence of nutrient elements of p and ba as well as other high productivity related elements such as cu zn and ni the moderate mo enrichment factor pr ph and low to moderate c p org ratios were an essential part of this organic preservation moreover the evidence we observed for the existence of hydrothermal activities consisted of high contents of quartz and pyrite large positive eu anomalies and enrichment of elements related to hydrothermal fluids hydrothermal influence may lead to similarities and fluctuations in water salinity organic productivity and preservation in the third es3 and first es1 members of the es hydrothermal fluids may play an essential role in promoting the development of high organic productivity stable reducing environment and brackish water as shown by the range of b ga and ts toc in the lakes during the source rock deposition this paper may provide implications for gas accumulation mechanisms and a complete set of organic and inorganic experimental data for source rock analysis in other lacustrine rift basins

high resolution cyclostratigraphic analysis from magnetic susceptibility in a lower kimmeridgian upper jurassic marl limestone succession la meouge vocontian basin france abstract high resolution magnetic susceptibility ms analysis was carried out on a lower kimmeridgian alternating marl limestone succession of pelagic origin that crops out at la meouge vocontian basin southeastern france the aim of the study was to characterize the strong dm scale sedimentary cyclicity of the succession at a very high resolution and to analyze the cycles for evidence of astronomical forcing from marl to limestone ms varies progressively and closely tracks the highest frequency cyclicity corresponding to the basic marl limestone couplets long term wavelength cycling modulates the high frequency cyclicity couplets and appears to be controlled by clay content spectral analysis of the ms record reveals the presence of the complete suite of orbital frequencies in the precession obliquity and eccentricity 95 128 ka and 405 ka bands with very high amplitude of the precession index cycles originating from dm scale couplets 405 ka eccentricity cycles are very pronounced in the ms maxima of the marl members of the couplets suggesting eccentricity driven detrital input to the basin 405 ka orbital tuning of the ms maxima further sharpens all of the orbital frequencies present in the succession these results are similar to those of previous studies at la meouge that used carbonate content observed in field our results are also in accordance with cyclostratigraphic studies in spain and canada that report dominant precession index forcing by contrast in the kimmeridge clay dorset uk obliquity forcing dominates cyclic sedimentation with weaker influence from the precession index ammonite zone duration estimates are made by counting the interpreted precession cycles and provide an ultra high resolution assessment of geologic time in sum this study demonstrates the power of the ms as a proxy in characterizing the high resolution cyclostratigraphy of mesozoic sections particularly in alternating marl limestone successions and for high resolution correlation and astronomical calibration of the geologic time scale

cyclostratigraphy orbital tuning and inferred productivity for the type kimmeridge clay late jurassic southern england three independently measured variables magnetic susceptibility photoelectric factor and total gamma ray obtained from throughout the type kimmeridge clay fm in dorset southern england were used to identify regular metre scale sedimentary cycles spectral analysis demonstrates that for long stratigraphical intervals the cycles are expressed as large amplitude cycles of 1 87 4 05 m wavelength and smaller amplitude cycles of around half that wavelength these cycles are interpreted to record orbital obliquity and precession respectively the much larger amplitude of the inferred obliquity cycles compared with the precession cycles may indicate a high latitude climatic forcing transferred to lower latitudes via sea level variations orbital tuning indicates that the early kimmeridgian sensu anglico lasted at least 3 6 ma 95 longer wavelength cycles and the late kimmeridgian at least 3 9 ma 103 longer wavelength cycles the first detailed productivity estimates for the kimmeridge clay fm on a cycle by cycle calculation indicate that average productivity of the type kimmeridge clay 220 g m 2 a 1 was less than the average productivity on modern continental shelves the high average organic carbon content of the type kimmeridge clay 3 8 total organic carbon cannot be attributed to high average productivity however the average organic carbon content is consistent with low siliciclastic mineral dilution of organic matter and or elevated preservation linked to reduced bottom water oxygenation

eclogite facies metamorphism in impure marble from north qaidam orogenic belt geodynamic implications for early paleozoic continental arc collision abstract in the north qaidam ultrahigh pressure uhp metamorphic belt impure marble and interbedded eclogite represent a particular sedimentary provenance and tectonic setting which have important implications for a controversial problem the dynamic evolution of early paleozoic subduction collision complexes in this contribution detailed field work mineral chemistry and whole rock geochemistry are presented for impure marble to provide the first direct evidence for the recycling of carbonate sediments under ultrahigh pressures during subduction and collision in the yuka terrane in the north qaidam uhp metamorphic belt according to conventional geothermobarometry pre peak subduction to 0 8 1 3 gpa 485 569 c was followed by peak uhp metamorphism at 2 5 3 3 gpa 567 754 c and cooling to amphibolite facies conditions at 0 6 0 7 gpa 571 589 c u pb dating of zircons from impure marble reveals a large group with ages ranging from 441 to 458 ma peak at 450 ma a smaller group ranging from 770 to 1000 ma peak at 780 ma and minor 1 8 ga zircon aged ca 430 ma uhp metamorphism the youngest detrital zircons suggest a maximum depositional age of ca 442 ma and a burial rate of ca 1 0 1 1 cm yr when combined with p t conditions and uhp metamorphic age the ree and trace element patterns of impure marble with positive sr and u anomalies negative high field strength elements nb ta zr hf and ti and ce anomalies imply that the marble had a marine limestone precursor impure marble intercalated with micaschist and eclogite was similar to limestone and siltstone protoliths deposited in continental fore arc or arc setting with basic volcanic activity therefore the yuka terrane most likely evolved in a continental island arc setting during the paleozoic these data suggest that metasediments were derived from a mixture of proterozoic continental crust and juvenile early paleozoic oceanic and or island arc crust in addition their protoliths were likely deposited in a terrigenous dominated forearc marine basin rather than an intracontinental basin environment further evidence that some continental arc volcanic rock may have been the source of eclogite in the north qaidam these sediments formed in a forearc basin close to the qaidam block to the north were transported in the subduction zone to 100 110 km depth with uhp metamorphism prior to exhumation meanwhile the new results suggest that subduction erosion occurred along the active continental margin during the qaidam block with north dipping subduction indicating that the north qaidam uhp metamorphic belt may have formed during continental arc collision

recognizing the albian cenomanian oae1d sequence boundary using plant carbon isotopes dakota formation western interior basin usa analysis of bulk sedimentary organic matter and charcoal from an albian cenomanian fluvial estuarine succession dakota formation at rose creek pit rcp nebraska reveals a negative excursion of 3 in late albian strata overlying cenomanian strata have 13c values of 24 to 23 that are similar to pre excursion values the absence of an intervening positive excursion as exists in marine records of the albian cenomanian boundary likely results from a depositional hiatus the corresponding positive 13c event and proposed depositional hiatus are concordant with a regionally identified sequence boundary in the dakota formation d2 as well as a major regressive phase throughout the globe at the albian cenomanian boundary data from rcp confirm suggestions that some positive carbon isotope excursions in the geologic record are coincident with regressive sea level phases we estimate using isotopic correlation that the d2 sequence boundary at rcp was on the order of 0 5 m y in duration therefore interpretations of isotopic events and associated environmental phenomena such as oceanic anoxic events in the shallow marine and terrestrial record may be influenced by stratigraphic incompleteness further investigation of terrestrial 13c records may be useful in recognizing and constraining sea level changes in the geologic record

fossil wood carbon isotope stratigraphy of the non marine wealden group lower cretaceous southern england fossil wood carbon isotope data are presented for the wessex formation a non marine unit within the lower cretaceous valanginian barremian wealden group of the isle of wight and dorset southern england the carbon isotope values have a range 13 c c 26 6 to 19 8 that is consistent with that expected for mesozoic c 3 plants consideration of the isle of wight fossil wood carbon isotope data together with data from dorset allows construction of a composite fossil wood carbon isotope curve for almost the entire wealden group the new carbon isotope curve is in smooth continuity with data previously published from the overlying lagoonal vectis formation and marine lower greensand group of aptian age a tentative correlation with a tethyan reference carbon isotope curve allows the provisional application of stage level chronostratigraphy to the wealden group correlations suggest that the wealden group sediments are dominantly of hauterivian and barremian age and that the valanginian is either condensed or partially missing the carbon isotope data presented indicate that even during times of relative carbon cycle quiescence atmosphere co 2 faithfully tracks the carbon isotopic composition of the oceanic reservoir

sedimentary and organic geochemical investigation of tertiary lacustrine oil shale in the central tibetan plateau palaeolimnological and palaeoclimatic significances article i nfo the zhuonai lake and lunpori oil shale located in the central tibetan plateau were deposited in a tertiary lacustrine environment in the hoh xil and lunpola basins respectively a combined investigation of sedimentary organic geochemistry and organic carbon isotope was performed to define source rock potential the palaeoenvironment and source of the organic matter three types of facies sequences are developed in the zhuonai lake section and oil shale mainly occurs in the oil shale marl sequence the oil shale silty claystone and oil shale marl facies sequences are developed in the lunpori section both oil shales are finely stratified especially for the lunpori oil shale with thickness of the laminae about 10 m which contains abundant pyrite crystals and fossilized fish bones both the zhuonai lake and lunpori oil shale contain high values of total organic matter toc s2 and hydrogen index hi indicating the oil shales have good oil source rock potential tmax values show an immature stage of organic matter for the zhuonai lake oil shale and thermally marginally mature for the lunpori oil shale because of difference in their burial history lunpori oil shale shows the characteristics of amorphous organic matter aom dominance odd over even predominance maximum n alkanes peak at nc25 or nc23 higher proportion of c29 sterane light 13 corg values 30 0 to 27 4 high concentrations of phytane pr ph ratio ranging from 0 02 to 0 18 high values of gammacerane index up to 25 26 and presence of carotane which are consistent with a reducing stratified and hypersaline palaeo lake with main contribution of algae and bacteria to the organic matter om oil shale samples from the lower and upper part of the zhuonai lake section are characterized by low h c ratios and high o c ratios amorphous humic om and vitrinite dominance odd over even predominance with long chain n alkanes dominance heavy organic carbon isotope and c29nc27 sterane distribution in agreement with a main contribution of land plant the heavy organic carbon isotope suggests the expanding of c4 land plant during the early miocene while the most samples show characteristics of aom dominance maximum peak at nc29 or nc31 and high c27 sterane concentration consistent with a main contribution from algae to the om the pr ph ratio cannot be applied as a measure for redox conditions in the section because of maturity effects biomarker analysis indicates that the salinity during the deposition of the zhuonai lake oil shale was not enhanced the oligocene lunpori oil shale and the early miocene zhuonai lake oil shale recorded the variation of palaeolimnological water chemistry the development history of the palaeo lakes from the oligocene saline to the early miocene fresh water reflects the variation of palaeoclimate from dry to humid in the central tibetan plateau

terrestrial carbon isotope records from coastal deposits algarve portugal a tool for chemostratigraphic correlation on an intrabasinal and global scale the carbon isotope signature of terrestrial organic matter om offers a valuable tool to develop stratigraphic correlations for near shore deposits a mid cretaceous coastal succession of the western algarve basin portugal displays a marked negative 13c excursion ranging from 21 2 to 27 8 in the early aptian followed by two shifts towards higher values up to 19 3 during the early and late aptian respectively the dominance of cuticle and leaf debris in the bulk om fraction is confirmed by optical studies rock eval pyrolysis and by comparison with the 13c signature of four different types of fossilized land plant particles correlation of two terrestrial 13cbulk om records from different study sites leads to a significant enhancement of the intrabasinal stratigraphic correlation within the algarve basin three prominent excursions in the portuguese records can be correlated with existing 13c curves from pelagic and terrestrial environments the general carbon isotope pattern is superimposed by small scale fluctuations which can be explained by compositional variations within the om

impact of the perturbation zonal velocity variation on the spatio temporal occurrence pattern of l band scintillation a case study the earlier evolved method for the forecast of the spatiotemporal variation of l band scintillation based on the expected variation of the perturbations under favorable ionospheric thermospheric conditions has been refined by duly accounting for the local time variation of the zonal velocity of the perturbations the unique combination of the two geostationary satellites gsat 8 and gsat 10 over the indian zone has been used to estimate the typical local time dependence of the perturbation velocities by closely following identifiable features in the scintillation pattern the measured velocities that registered a steady decrease with the progression of night had been shown to significantly alter the forecast pattern of the scintillations with respect to longitude and local time the significant improvement in the forecast pattern has been demonstrated through a case study putting the forecast method on a firmer footing

stability of the astronomical frequencies over the earth s history for paleoclimate studies the expected changes over the past 500 million years in the principal astronomical frequencies influencing the earth s climate may be strong enough to be detectable in the geological records and such effects have been inferred in several cases calculations suggest that the shortening of the earth moon distance and of the length of the day back in time induced a shortening of the fundamental periods for the obliquity and climatic precession from 54 to 35 41 to 29 23 to 19 and 19 to 16 thousand years over the last half billion years at the same time the precessional constant increased from 50 to 61 arc seconds per year the changes in the frequencies of the planetary system due to its chaotic motion are much smaller their influence on the changes of the periods of climatic precession obliquity and eccentricity of the earth s orbit around the sun can be neglected eccentricity periods used for quaternary climate studies may therefore be considered to have been more or less constant for pre quaternary times

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

equatorial ionospheric electric fields during the november 2004 magnetic storm 1 we use radar measurements from the jicamarca radio observatory magnetometer observations from the pacific sector and ionosonde data from brazil to study equatorial ionospheric electric fields during the november 2004 geomagnetic storm our data show very large eastward and westward daytime electrojet current perturbations with lifetimes of about an hour indicative of undershielding and overshielding prompt penetration electric fields in the pacific equatorial region during the november 7 main phase of the storm when the southward imf the solar wind and reconnection electric fields and the polar cap potential drops had very large and nearly steady values this result is inconsistent with the recent suggestion that solar wind electric fields penetrate without attenuation into the equatorial ionosphere for several hours during storm main phase the largest daytime prompt penetration electric fields about 3 mv m ever observed over jicamarca occurred during the november 9 storm main phase when large equatorial electrojet current and drift perturbations were also present in the pacific and brazilian equatorial regions the rise and decay times of these equatorial electric fields were about 20 min longer than of the corresponding solar wind electric fields the ratios of prompt penetration electric fields and corresponding solar wind electric field changes were highly variable even during the day and had largest values near dawn also the prompt penetration electric fields did not show polar cap potential drop saturation effects our results clearly highlight that the relationships of prompt penetration and solar wind electric fields and polar cap potentials are far more complex than implied by simple proportionality factors

comprehensive stable isotope investigation of marine biogenic apatite from the late cretaceous early eocene phosphate series of morocco fossil biogenic apatites were studied for their geochemical composition across the late cretaceous early eocene moroccan phosphate series in the ouled abdoun and ganntour basins in morocco in order to characterize paleoenvironmental conditions and to improve stratigraphy the vertebrate remains show particularly good structural mineralogical and chemical preservations which relate to the favorable depositional environment of the phosphorite the main studied fossils shark tooth enameloid and dentine and coprolites show large range in 13c values from 14 to 6 which can be coupled to different carbon sources enameloid yielded mostly positive 13c isotopic compositions that are comparable with values reported from modern teeth coprolites have the lowest 13c values that reflect burial conditions with intensive organic matter recycling the large variation in 18opo4 values of the shark teeth can be related to ecological differences however the mean 18opo4 data reflect important temporal variation along the series together with the corresponding average 13c values comparisons with the global isotope records allow identifying the early eocene climatic optimum in the top of the ouled abdoun series above bed 0 the isotope data further suggest a sedimentary gap during the latest thanetian and the paleocene eocene thermal maximum the top of the paleocene series bed iia can be dated to late selandian early thanetian with the recognition of the early late paleocene event elpe the eritherium bone bed that yielded the earliest known placental mammals from africa would be located below the elpe and therefore cannot be younger than late selandian the isotope data from the older paleocene bed iib and cretaceous upper bed iii beds in the ouled abdoun basin can be correlated with the latest danian early selandian and the latest maastrichtian global isotope record respectively based on the 18opo4 data the cretaceous layers of the ganntour basin cover most of the maastrichtian period except the very early part all these early paleogene and cretaceous chemostratigraphic ages however need further confirmations from other proxies yet the interpretations are in general agreement with the biostratigraphy derived from the selachian fauna

carbon isotope analysis of fossil wood and dispersed organic matter from the terrestrial wealden facies of hautrage mons basin belgium pedogenic nodules calcitic shells dispersed organic carbon and bulk rocks affected by low diagenesis are judged to be reliable tools for carbon isotope chemostratigraphy up to now no systematic study has been carried out to check the reliability of fossil wood material for carbon isotope chemostratigraphy in terrestrial settings the 235 m thick wealden facies sediments of the danube bouchon quarry at hautrage hautrage clays formation mons basin belgium encompass dark to grey clays and sands rich in organic matter and coalified charcoalified fragments of fossil wood deposited in an alluvial plain during middle barremian to earliest aptian we measured and compared the carbon isotope ratios of 110 levels of the stratigraphic succession for dispersed organic carbon delta c 13 doc and fossil wood delta c 13 wood collected in the same geological level in the whole succession the averages of delta c 13 doc and delta c 13 wood have a significant difference of about 0 9 the delta c 13 wood is usually heavier than the delta c 13 doc which is consistent with measurements on different constituents of modern trees branches versus leaves and tissues in one single stratigraphic level the variability of delta c 13 wood is much higher up to 7 3 parts per thousand than that of delta c 13 doc 0 4 parts per thousand four main causes may explain these results firstly the delta c 13 doc averages the isotopic signal of different compounds and tissues such as leaves seeds cuticles as they become mixed and dispersed the delta c 13 wood reflects the carbon isotope ratio of a small part only of one single tree which is a complex system with delta c 13 variations over a range of 4 parts per thousand secondly there is strong delta c 13 variability between different species of plants in hautrage several gymnosperm genera were collected including podocarpoxylon taxodioxylon brachyoxylon and thujoxylon and numerous fern taxa thirdly coalification and charcoalification can affect the delta c 13 of the doc and the various kinds of woods in a different way fourthly the wood fragments may be reworked several times from more ancient geological levels especially in the alluvial plain environment of hautrage where thick levels of fluviatile coarse sand deposits are observed however in the whole succession both delta c 13 wood and delta c 13 doc curves show similar trends this suggests that carbon isotope curves on fossil wood can be matched to carbon isotope curves on doc for the whole trend fossil wood is a relatively good chemostratigraphic tool when sufficient samples are measured in the succession whenever possible both control of the wood taxa and estimation of degree of char coalification are however recommended in one single level charcoal has more stable delta c 13 wood values than delta c 13 wood of coalified fragments the delta c 13 positive trend can be due to several causes including global pco 2 variations and or regional changes and or local environmental conditions in the alluvial plain if global the dating of the hautrage succession may be refined to the late early barremian early late barremian by matching palynological and carbon isotope chemostratigraphical data c 010 elsevier b v all rights reserved

role of imf b y in the prompt electric field disturbances over equatorial ionosphere during a space weather event on 7 january 2005 a p 40 prompt penetration electric field perturbations of opposite polarities were observed over thumba and jicamarca on a few occasions during 13 45 16 30 ut however the electric field was found to be eastward during 14 45 15 30 ut over both thumba and jicamarca contrary to the general expectation wherein opposite polarities are expected at nearly antipodal points on closer scrutiny three important observational features are noticed during 14 10 15 15 ut first during 14 10 14 45 ut despite increasing southward interplanetary magnetic field imf b z condition the already westward electric field over thumba weakened less westward while the eastward electric field over jicamarca intensified more eastward second the electric field not only became anomalously eastward over thumba but also got intensified further during 14 45 15 00 ut similar to jicamarca third during 15 00 15 15 ut despite imf b z remaining steadily southward the eastward electric field continued to intensify over thumba but weakened over jicamarca it is suggested that the changes in imf b y component under southward imf b z condition are responsible for skewing the ionospheric equipotential patterns over the dip equator in such a way that thumba came into the same dp2 cell as that of jicamarca leading to anomalous electric field variations magnetic field measurements along the indian and jicamarca longitude sectors and changes in high latitude ionospheric convection patterns provide credence to this proposition thus the present investigation shows that the variations in imf b y are fundamentally important to understand the prompt penetration effects over low latitudes

application of an eutrophic lake model to the origin of ancient organic carbon rich sediments in this paper we approach the problem of the origin of organic carbon rich sediments by using an integrated isotopic and organic geochemical study of the annual productivity eutrophication cycle in the water column of lake greifen switzerland and the historical expression of such cycles as found in the sediments the lake greifen water column and sediment studies reveal that 13c carbonate organic matter is correlated with the hydrogen indices hi of kerogens explicable in terms of changing productivity and preservation of the organic matter and the co2 budget of the water body the lake model implies that if high productivity in co2 limited surface waters high nutrient co2 ratio was controlling the preservation of organic matter a correlation between decreasing 13c carbonate organic matter and increasing hi values may be observed in contrast if low to moderate productivity in co2 unlimited surface waters low nutrient co2 ratio where bottom water anoxia promotes the preservation of organic matter a correlation between increasing 13c carbonate organic matter and increasing hi values may be observed application of this model to two well known jurassic sequences gave a correlation of increasing hi values with decreasing 13c carbonate organic matter for the kimmeridge clay formation united kingdom and increasing hi values with increasing 13c carbonate organic matter for the early toarcian shales france this suggests that the controlling factor of the former deposit was high primary bioproductivity and of the latter deposit anoxic bottom water conditions

integrated stratigraphy of a continental pliensbachian toarcian boundary lower jurassic section at taskomirsay leontiev graben southwest kazakhstan during the early jurassic major palaeoclimatic changes associated with large carbon cycle perturbations occurred at the pliensbachian toarcian boundary although the detailed marine palaeoclimatic record of this time interval and its impact on the marine biota is well recorded much less is known about the continental realm the current study documents new palynological and high resolution carbon isotope data measured on bulk organic matter from the continental lower jurassic section of taskomirsay in kazakhstan central asia both datasets allow a transition zone between the pliensbachian and toarcian to be identified in addition the spore and pollen distribution suggests a warming trend from the pliensbachian to the toarcian most probably associated with a shift in floristic associations from the siberian to the sino european palaeofloristic provinces as recorded elsewhere in central asia during the early jurassic the taskomirsay section is thus of primary interest for palaeoclimatic studies as it is one of the very few well dated continental section worldwide that records the pliensbachian toarcian palaeoclimatic changes

low latitude ionospheric thermospheric response to storm time electrodynamical coupling between high and low latitudes 1 using multi instrumental and multistation data we present low latitude ionospheric thermospheric behavior during the geomagnetic storm of 15 may 2005 the diurnal pattern of total electron content tec at a chain of equatorial to low latitude stations shows strong positive ionospheric storm on 15 may latitudinal variation of tec shows development of strong equatorial ionization anomaly eia on the same day evidence in terms of equatorial electrojet eej and magnetogram signatures is presented for the prompt penetration of interplanetary electric field ief as the cause of the positive ionospheric storm consequent to the storm time circulation resulting from the extra energy deposition via joule heating over high latitudes compositional changes occur in the global thermosphere tec enhancements on 16 may are attributed to enhancement of atomic oxygen at equatorial and low latitudes and the negative ionospheric storm on 17 may observed beyond certain low latitudes is explained in terms of enhancement of molecular species because of the storm time neutral composition changes strong esf plume structures on range time intensity rti map and l band scintillation and tec depletions in gps measurements are observed in the longitude sectors where the local time of sudden storm commencement ssc falls after the post sunset hours the ionospheric zonal electric fields are altered by the combined effects of eastward disturbance dynamo electric fields and direct prompt penetration of eastward electric fields associated with the northward turning of interplanetary magnetic field imf bz leading to subsequent development of esf after midnight

terrestrial record of methane hydrate dissociation in the early cretaceous reconstruction of changing c isotopic composition of early cretaceous atmospheric co2 from fossilized c3 vascular land plant tissue revealed a brief and striking negative excursion d 25 in atmospheric d 13 c followed by a rapid positive compensation d 15 during the aptian ca 117 ma mass balance calculations show that dissociation of a small amount of methane gas hydrate is the most tenable cause of the negative excursion this would also result in an increased co2 o2 mixing ratio as o2 is consumed during ch4 oxidation to co2 spurring the exponential phase of angiosperm biogeographic expansion

major environmental changes recorded by lacustrine sedimentary organic matter since the last glacial maximum near the equator lagoa do caco ne brazil sediment samples collected along a 6 m core drilled in the deepest part of the lagoa do caco ne brazil have been investigated in order to determine source s and degradation conditions of the organic matter om with special emphasis on paleoenvironmental implications bulk organic geochemistry rock eval pyrolysis c n determination 13c and 15n measurement and petrography combined with sedimentological evidence and radiocarbon dates allowed to identify four major intervals documenting major environmental changes that occurred during the last 20 000 years the first interval dating back to the end of the last glacial maximum lgm contains well preserved om derived from higher plants this material was most probably produced in an ephemeral palustrine system and rapidly buried by sands this level is thought to have been deposited under relatively arid climate conditions associated with strong but episodic rainfalls between 19 240 and 17 250 cal years bp the climate appears to have been more humid and seasonality more pronounced as suggested by the presence of a permanent lake after a drastic environmental change dating back to 17 250 cal years bp the sediment became truly lacustrine with restricted mineral input and highly degraded higher plant derived organic matter after that a stepwise improvement in the preservation of om occurred as revealed by several pronounced shifts in the rock eval tps2 signal these changes could document abrupt climatically driven changes during the late glacial finally around 5610 cal years bp environmental conditions approaching those prevailing today were established minor climatic changes during the holocene were probably buffered by a high water table which might explain the lack of paleoenvironmental fluctuations

orbital tuning of a lower cretaceous composite record maiolica formation central italy 1 a high resolution pelagic bulk carbonate stable isotope record from a central tethyan lower cretaceous composite section is presented three well exposed sedimentary sequences chiaserna monte acuto bosso and gorgo a cerbara sections central italy cropping out throughout the maiolica formation were correlated by a detailed magnetostratigraphy lithostratigraphy and calcareous plankton biostratigraphy in order to reconstruct a continuous composite record from the middle berriasian to the lower aptian the integrated stratigraphy of the three sequences provided an accurate time framework for the new high resolution c isotope curve which is presented in this study the composite 13c signal recorded in the depth domain was analyzed by combined lomb scargle periodogram and weighted wavelet z transform wwz weighted wavelet amplitudes wwa foster wavelet spectral methodologies both appropriate for unevenly sampled curves these tools allowed us to unravel the main frequencies modulating the record and their hypothetical shift in depth respectively the long term 400 000 and 2 400 000 years eccentricity cycles were consistently recorded throughout all the composite record once band pass filtered in these two periodicity bands and compared to the lithologic pattern cycles identified throughout the composite sequence the 13c signal was used as a valuable proxy record for a reliable construction of an orbital tuning of the early cretaceous an estimated age for all the different stratigraphic events recognized throughout the composite record was reported in particular the reestimated ages of the paleomagnetic chrons documented in the upper part of the record show differences with those reported by gradstein et al 2004 up to 2 m y the valanginian carbon shift present in the middle part of the composite sequence was estimated to be 2 3 m y long the good agreement between the estimated age of the base of this positive carbon isotope excursion 136 34 m y and the predominant volcanic phase associated to the parana etendeka large igneous province intrusion confirmed a possible cause effect link between the two events

palaeoenvironmental reconstruction of lacustrine source rocks in the lower 1st member of the shahejie formation in the raoyang sag and the baxian sag bohai bay basin eastern china abstract the lower 1st member es1l of the oligocene shahejie formation is the most important source rock interval in the raoyang sag and the baxian sag to reveal the controlling factors that affected the distribution of organic rich source rocks we analyzed the lower es1 es1l samples collected from the raoyang sag and the baxian sag using sedimentological and geochemical techniques to reconstruct the lacustrine palaeoenvironmental conditions most of the samples had chemical index of alteration cia values between 70 and 75 which reflect a stable and moderately weathered source under a transitional climate the distribution of depocenters and palaeo water depths indicated that the main catchment area was concentrated in the raoyang sag with a maximum palaeo water depth of 14 m and a wave base depth of 7 5 m stable isotope data from carbonates 18ocarb and 13ccarb showed that the lakes with long residence times in the raoyang sag had a positive correlation and that the lakes with short residence times in the baxian sag had no isotopic covariance during the deposition of the lower es1 the p al and p ti ratios ptotal and carbon isotope values of the organic matter 13corg in the two sags illustrated stable palaeoproductivity without much fluctuation the enrichments of mo u and ratios of c p org b ga and sr ba further indicated saline and anoxic bottom water conditions associated with stable water column stratification in well xi63 and brackish and less anoxic bottom water conditions in well nd1 during the deposition of the main source rock of the lower es1 moreover the plots of mo and u enrichment versus toc and hydrogen index values versus 13c i e the difference between the 13c values of carbonates and organic matter corroborated the inference that the preservation of organic matter was the main factor controlling the formation of organic rich source rocks in the raoyang sag and the baxian sag during the deposition of the lower es1

global equatorial plasma bubble occurrence during the 2015 st patrick s day storm an analysis of the occurrence of equatorial plasma bubbles epbs around the world during the 2015 st patrick s day geomagnetic storm is presented a network of 12 global positioning system receivers spanning from south america to southeast asia was used in addition to colocated vhf receivers at three stations and four nearby ionosondes the suppression of postsunset epbs was observed across most longitudes over 2 days the epb observations were compared to calculations of the linear rayleigh taylor growth rate using coupled thermosphere ionosphere modeling which successfully modeled the transition of favorable epb growth from postsunset to postmidnight hours during the storm the mechanisms behind the growth of postmidnight epbs during this storm were investigated while the latter stages of postmidnight epb growth were found to be dominated by disturbance dynamo effects the initial stages of postmidnight epb growth close to local midnight were found to be controlled by the higher altitudes of the plasma i e the gravity term modeling and observations revealed that during the storm the ionospheric plasma was redistributed to higher altitudes in the low latitude region which made the plasma more susceptible to rayleigh taylor growth prior to the dominance of the disturbance dynamo in the eventual generation of postmidnight epbs

carbon isotope composition of lower cretaceous fossil wood ocean atmosphere chemistry and relation to sea level change the carbon isotope composition of fossil wood fragments collected through a biostratigraphically well constructed aptian lower cretaceous shallow marine siliciclastic succession on the isle of wight southern britain shows distinct variations with time the results indicate that the stratigraphic signature of delta sup 13 c sub wood through the aptian was influenced primarily by fluctuations in the isotopic composition of co sub 2 in the global ocean atmosphere system as registered in marine carbonates elsewhere and was not governed by local paleoenvironmental and or paleoecological factors negative and positive excursions in delta sup 13 c sub wood through the lower aptian occur in phase with inferred transgressions and regressions respectively a pattern that contrasts with that observed in many previous studies for different time intervals the relationship between delta sup 13 c variations and relative sea level change is tentatively interpreted as a response to various climatic and eustatic factors relating to rapid sea floor spreading thermal uplift of ocean floor emplacement of plateaus volcanic co sub 2 emissions weathering and sedimentary rate

effects of chemical preparation protocols on δ13c values of plant fossil samples abstract for over a half century studies of the stable carbon isotope compositions of plant fossils have provided noteworthy conclusions about the evolution of earth climate however different preparation protocols were used prior to carbon isotope analysis of plant fossils and the accuracy of measured 13c 12c ratios may strongly depend on them we have applied the most frequently used chemical preparation protocols to frenelopsis leaves from four cretaceous localities of western europe our results indicate that procedures to extract plant fossils from sediments are not adequate to retrieve the original plant 13c values the use of schulze s reagent to bleach cuticles in paleobotany allows misleading 13c values of specimens from a same locality with positive shifts of up to 13 6 and increases intra specimen and inter specimen variances sample treatment involving hcl or hcl hf gives consistent 13c mean values for a same leaf and for leaves from a same sedimentary bed however although hf does not provide any advantage in removing potential contamination sources it alters plant fossil tissues slightly increasing the intra and inter leaf variances of 13c values our results indicate that processing plant fossils with hcl only is the most accurate and conservative way to retrieve original 13c values

characteristics of the equatorial plasma drifts as obtained by using canadian doppler ionosonde over southern tip of india we present here characteristics of the doppler drift measurements over tirunelveli 8 73 n 77 70 e dip 0 5 n an equatorial site over southern india using doppler interferometry technique of canadian ionosonde three dimensional bulk motions of the scatterers as reflected from the ionosphere are derived by using doppler interferometry technique at selected frequencies using spaced receivers arranged in magnetic e w and n s directions after having compared with lowell s digisonde drifts at trivandrum we studied the temporal and seasonal variabilities of quiet time drifts for the year 2012 the observations showed higher vertical drifts during post sunset in the equinox followed by winter and summer seasons the comparison of doppler vertical drifts with the drifts obtained from a virtual height and b fejer drift model suggests that doppler vertical drifts are relatively higher as compared to the drifts obtained from model and virtual height methods further it is seen that vertical drifts exhibited equinoctial asymmetry in prereversal enhancement quite similar to such asymmetry observed in the spread f in the ionograms and gps l band scintillations the zonal drifts on the other hand showed westward during daytime with mean drifts of 150 200 m s and correlated well with equatorial electrojet strength indicating the role of e region dynamo during daytime while they are eastward during nighttime with mean drifts of 100 m s resembling f region dynamo process also zonal drifts showed large westward prior to the spread f onset during autumn equinox than vernal equinox suggesting strong zonal shears which might cause equinoctial asymmetry in spread f

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

low latitude ionospheric disturbance electric field effects during the recovery phase of the 19 21 october 1998 magnetic storm 1 low latitude ionospheric electric fields and currents are often strongly disturbed during periods of enhanced geomagnetic activity these perturbations can last for several hours after geomagnetic quieting we use incoherent scatter radar measurements from jicamarca and arecibo during 19 21 october 1998 to study for the first time the low latitude disturbance electric fields during the recovery phase of a large magnetic storm on 19 october the jicamarca data showed initially large and short lived time scale of about 10 20 min upward and westward drift perturbations in the early afternoon sector due to the penetration of strong magnetospheric electric fields probably driven by an increase in the solar wind dynamic pressure following the decrease of auroral activity very strong afternoon and nighttime zonal and vertical disturbance dynamo drifts were observed over jicamarca but surprisingly only small and sporadic perturbation drifts were present over arecibo the latitudinal variation of the daytime zonal disturbance dynamo drifts during this day is in good agreement with that previously observed for thermospheric disturbance winds the disturbance dynamo drifts also indicate significantly different local storm time and possibly latitudinal dependences for their vertical perpendicular and zonal drift components suggesting large variations in both the amplitude and direction of the disturbance dynamo electric field vector in the next day during moderately disturbed conditions the daytime perturbation drifts were small but following transient increases in geomagnetic activity large upward perpendicular drifts were observed near dusk over jicamarca and arecibo where simultaneous westward perturbation drifts were also seen these perturbations are consistent with the occurrence of strong prompt penetration electric fields reaching the magnetic equator the measured prompt penetration drift patterns are generally in good agreement with predictions from global convection models later at night under moderately disturbed conditions relatively large zonal and meridional disturbance dynamo electric fields were observed by the two radars our results illustrate the large variability of the low latitude perturbation electric fields relative to their climatological values after large storms probably due to the importance of additional disturbance processes they also indicate that a much deeper understanding of solar wind magnetospheric ionospheric processes is required for accurate predictions of these electric fields

new perspective on aptian carbon isotope stratigraphy data from δ13c records of terrestrial organic matter carbon isotope analyses were performed on detrital woody materials in aptian mid cretaceous marine sediments of central hokkaido northern japan a positive 13cwood excursion from 25 4 to 21 8 following a remarkable negative isotope shift is recognized in the early aptian and a small positive anomaly is also found in the latest aptian this 13cwood profile is exactly in phase with the 13ccarbonate curve from a pacific guyot when the age of the guyot carbonates is revised using published sr isotope stratigraphies the highly conformable 13c profiles of pacific and hokkaido sections suggest that 13c compositions of aptian marine and terrestrial carbon reservoirs changed simultaneously by the same amplitude within the ocean atmosphere biosphere system fluctuation patterns of tethyan 13ccarbonate curves are slightly different from those of pacific and hokkaido sections such differences in 13c profiles may be attributed to the local paleoceanographic setting of the aptian mediterranean tethys

paleomagnetic calibration of milankovitch cyclicity in lower cretaceous sediments abstract bedded pelagic limestones of early to mid cretaceous age may record cyclic climate variability driven by changes in the earth s orbit milankovitch cycles if properly calibrated the lithologic cycles could provide sedimentary chronometry at far shorter time scales than biostratigraphy and magnetic stratigraphy the lower cretaceous maiolica formation of northern and central italy displays rythmic bedding in sections whose magnetic reversal sequence is clearly correlated to the upper m series marine anomalies the magnetic reversals divide measured sections into 0 5 2 myr increments in which sedimentation rate assuming continous deposition can be measured to 15 25 accuracy paleomagnetically estimated sedimentation rates over a number of polarity zones establish with one exception a narrow range in periods of the carbonate cycles carbonate couplets have an estimated mean period of 23 5 kyr and prominent modulations in bedding thickness bundling have a mean period of 117 kyr kent and gradstein 1985 time scale the close match of sedimentary periodicities to orbital repeat times implies that the carbonate cycles reflect a combination of professional and eccentricity climatic forcing comparison of measured sections from different locations shows that bed to bed correlations are possible regionally cosistent with the milankovitch hypothesis episodes of barremian black shale deposition occur in the troughs of the short eccentricity cycle as roughly one half of the carbonate marl couplet or about 10 kyr duration it is possible to estimate both the timing relative to the top of reversed chron m 0 and duration of a period of unusual organic carbon rich deposition selli horizon in the early part of the cretaceous long normal magnetic polarity interval by tracing the sedimentary cycles up from the barremian strata

first observation of interhemispheric asymmetry in the epbs during the st patrick s day geomagnetic storm of 2015 in this work we have studied the characteristics of epbs such as their zonal drift and tilt from the low latitude and dip equatorial region in the indian longitude sector during the main phase of the 17 march 2015 storm all sky airglow imaging observations from tirunelveli 8 7on 77 8oe geographic 1 7on dip latitude and kolhapur 16 7on 74 3oe geographic 11 5on dip latitude are utilized here on 17 march 2015 epbs were observed to drift eastward during 14 30 16 30 ut between 3os and 15on dip latitudes a westward drift presumably under the influence of the disturbance dynamo electric field ddef initially appeared at higher dip latitudes almost 10 hours after the storm onset and subsequently the same was observed at lower dip latitudes the epbs attained a peak westward drift at 17 00 ut followed by a gradual decrease in their speed till 18 30 ut after regaining their westward speed the epbs continued to drift westward till 22 00 ut moreover a latitudinal gradient in the drift motion of the epbs was also observed on this night another interesting observation made from the images obtained from tirunelveli was the presence of a large westward tilt of the epbs the most intriguing finding of this study however was the asymmetry in the tilt of the epbs at conjugate points during the pre midnight hours on 17 march 2015 in this study the possible mechanisms that can explain these observations are discussed in the light of the current understanding of the equatorial electrodynamics and epbs

gypsum karstification induced subsidence effects on alluvial systems and derived geohazards calatayud graben iberian range spain abstract the karstification of the tertiary gypsum formations in the calatayud graben has given rise to synsedimentary and postsedimentary subsidence phenomena in both the neogene sediments of the endorheic graben fill and in the quaternary alluvial sediments deposited under exorheic conditions in the so called maluenda and perejiles areas covering 4 4 and 12 km 2 respectively the neogene sedimentary units stratigraphically above the gypsum have subsided due to the karstification of the underlying evaporites the maximum subsidence in both areas has reached at least 200 m the jalon jiloca perejiles alluvial system has been affected by karstic subsidence during its quaternary evolution ten stepped alluvial levels pediment terrace have been identified as a consequence of synsedimentary karstic subsidence the deposit of an alluvial level can be locally thickened changing in a short distance from less than 10 m to more than 100 m in thickness thus the deposit of an individual terrace can be locally superimposed on the deposits of older terraces the palaeokarst recorded in the sediments of the different alluvial levels shows how the karstic subsidence has controlled the dynamics of the sedimentary system the alluvial karstic subsidence is currently active in the flood plains affecting fluvial channels buildings communication ways irrigation ditches and the calatayud gypsum scarp