Genetic features of gas-condensate reservoirs in the Kekeya Field,southwest depression in the Tarim Basin,China

Oils, condensates and natural gases in the Kekeya Field, southeast depression of the Tarim Basin were studied for their geochemical characteristics. According to the distribution analysis of the C₂/C₃ values with C₁/C₂ values, C₂/C₃ values with C₁/C₃ values, as well as C₂/C₃ values with dryness index, there are two different types of natural gases in the studied field, which are spatially regularly distributed. One is the oil cracking gas, located on shallow reservoirs over X ²₅ reservoir, namely Upper oil legs; the other is kerogen cracking gas, located on X ²₇ reservoirs, X₈ reservoirs and E₂ k reservoirs, namely Lower oil legs. In addition, the distribution patterns of molar concentration of oils and condensates with different carbon numbers of the n-alkanes in the Kekeya Field indicate that the crude oils have experienced several kinds of secondary alterations, which were closely related to the charging of gaseous hydrocarbons after petroleum accumulation. These results indicate that, based on the research of δ ¹³C values of individual hydrocarbons, heptane values and isoheptane values of light hydrocarbons and aromatic maturity parameters for oils, condensates and natural gases, oils and gases were charged at different geological time in the Kekeya Field.

     

大型浅水湖泊与大气之间的动量和水热交换系数——以太湖为例

湖泊水面与大气之间垂直方向的动量、水汽和热量通量与风速、湿度和温度梯度之间存在比例关系,因此在湖泊水-气相互作用研究中,这比例系数(交换系数)是关键因子.在以往的研究中,交换系数通常直接采用水面梯度观测法或海洋大气近地层的参数化方案进行计算.本文采用涡度相关系统和小气候系统仪器在太湖平台上直接观测的通量和气象要素,对上述交换系数(最小均方差原则)进行优化,结果为:动量交换系数C_D10N=1.52×10^-3、水汽交换系数C_E10N=0.82×10^-3、热量交换系数CH10N=1.02×10^-3,与其他内陆湖泊涡度相关观测数据的推导结果一致.本文的研究结果表明:与海洋参数化方案相比,在相同的风速条件下,湖面的空气动力学粗糙度比海洋高,这可能是由于受到水深的影响;如果采用海洋参数化方案,会导致湖泊年蒸发量的估算值偏大40%.太湖的动量、水汽和热量交换系数可以视为常数,可以不考虑稳定度和风速的影响.这是因为本文中83%的数据为近中性条件.敏感性分析表明:如果考虑稳定度的影响,LE模拟值的平均误差降低了0.5 W/m²,H的平均误差降低了0.4 W/m²,u*的计算值没有变化;如果考虑风速的影响,u*模拟值的平均误差降低了0.004 m/s,LE的平均误差升高了1.3 W/m²,H的模拟结果几乎不受影响.这一结果能为湖气相互作用研究提供参考.     

The use of MRS in the determination of hydraulic transmissivity: The case of alluvial aquifers

Magnetic Resonance Sounding (MRS) is nowadays accepted as a new geophysical method that can be used for a reliable determination of the ground water content distribution in the top 150 m. A great effort has also been made in MRS development to deduce the hydraulic transmissivity, based on empiric relationships of the permeability with a factor F which is calculated with NMR parameters measured at laboratory scale. To use this relationship under field conditions a calibration coefficient C_T = T_pt / F has to be previously established, which demands the knowledge of the transmissivity T_pt evaluated in the pumping test. The transmissivity can then be calculated at any other site of the same aquifer using the relation T_mrs = C_TF. The C_T values reported suggest a certain relationship with the lithology, but with a great dispersion and contradictory results. MRS surveys carried out in alluvial aquifers in Spain have shown that the value of C_T evaluated at one site may not be valid at another place of the same aquifer, because of the great heterogeneity of this kind of geological environment. The demand of a pumping test at each site where a MRS is measured invalidates the method actually used for MRS transmissivity evaluation. More than 50 MRS have been used to propose a new methodology. The aquifers visited cover a great range of transmissivities (from 2 × 10^− 6 to 9 × 10^− 3 m²/s). The MRS signal amplitude varies between 20 and 1400 nV, the signal/noise ratio is in the range from 0.6 to 42, and the value of the decay time constant varies from 200 to 800 ms. It has been demonstrated that when the transmissivity increases, the value of F decreases, and C_T increases, except for certain groups of MRS taken at the same aquifer or part of one aquifer, for which F increases with T_pt, keeping C_T constant. A function C_T(F) of the type C_T = mF^− n has been obtained that allows the transmissivity evaluation without the need of T_pt. Considering that both values of transmissivity, T_pt and T_mrs, are subjected to deviations due to the experimental errors as well as due to evaluation errors, the prediction achieved by the proposed equation is rather good. To perform a better evaluation of the values of the coefficients m and n it is necessary to have a greater number of MR soundings of good quality and with a trustworthy inversion at locations where a really comparable and good performed pumping test is available, covering a sufficient range of transmissivities. Though the data we have used do not always fulfil these conditions, the result is promising. Once a trustable function is available, the forecast of the transmissivity using MRS will not need the existence of any pumping test in the area. The general extension of this methodology demands the availability of MRS taken at all kinds of geological and hydrogeological environments, which is impossible without the existence of a universal MRS data base.     

Distribution and significance of C~_(40) alkanes in the extracts of Cretaceous source rocks from the Songliao Basin

Source rock extracts and crude oils from the Songliao Basin were analyzed by high-temperature gas chromatography (HTGC), gas chromatography-mass spectrometry (HTGC-MS) and gas chromatography-isotope ratio-mass spectrometry (GC-IRMS), for high molecular-weight alkanes. The distributions of n-alkanes in the Nenjiang Formation extracts are in the C14―C63 range; a bimodal distribution occurs in the C-21 and C21―40 regions. The C30―C37 n-alkanes are accompanied by C29―C35 hopanes, whereas the high molecular-weight C45―C47 n-alkanes co-occur with abundant isoalkanes, alkylcyclohexanes and alkylcyclopentanes. The high δ 13C values of the n-alkanes and the microscopic maceral compositions indicate a highly diversified organic source input for the Nenjiang Formation source rocks, ranging from aquatic plants, blue alge-bacteria, to land plant material. In contrast, n-alkanes in the rock extracts of the Qingshankou Formation are characterized by a single modal distribution, with relatively low abundances of C29―C35 hopanes, but high molecular-weight isoalkanes, alkylcyclohexanes and alkylcyclopentanes. The relatively low δ 13C values of C22―C44 n-alkanes and organic material compositions indicate that the source rocks in the Qingshankou Formation contain dominantly type I algal organic matter. The relative abundance of C 40 compounds in source rocks changes little at low maturity stage, but decreases drastically at higher maturity levels, with a concurrent reduction in the odd/even carbon predominance. In crude oils, in contrast, the relative abundance of C 40 compounds appears to relate closely with the oil source and oil viscosity.     

Capacity-based inelastic displacement spectra for reinforced concrete bridge columns

Capacity-based inelastic displacement spectra that comprise an inelastic displacement ratio (C_R ) spectrum and the corresponding damage index (DI ) spectrum are proposed in this study to aid seismic design and evaluation of reinforced concrete (RC) bridges. Nonlinear time history analyses of single-degree-of-freedom (SDOF) systems are conducted using a versatile smooth hysteretic model when subjected to far-field and near-fault ground motions. It is demonstrated that the Park and Ang damage index can be a good indicator for assessing the actual visible damage condition of columns regardless of its loading history, providing a better insight into the seismic performance of bridges. The computed spectra for near-fault (NF) ground motions show that as the magnitude of pulse period ranges increases from NF1 (0.5-2.5 seconds) to NF2 (2.5-5.5 seconds), the spectral ordinates of the C_R and DI spectra increase moderately. In contrast, the computed spectra do not show much difference between NF2 and NF3 (5.5-10.5 seconds) when the period of vibration T_n≤  1.5 seconds, after which the spectral ordinates of NF3 tend to increase obviously, whereas those of NF2 decrease with increasing T_n . Moreover, when relative strength ratio R  = 5.0, nearly all of the practical design scenarios could not survive NF3. On the basis of the computed spectra, C_R and DI formulae are presented as a function of T_n , R , and various design parameters for far-field and near-fault ground motions. Finally, an application of the proposed spectra to the performance-based seismic design of RC bridges is presented using DI as the performance objective.     

Microwave anomalous propagation (AP) measurement over Akure South-Western Nigeria

Anomalous propagation (Anaprop) of microwave radiation is known to be caused by several meteorological conditions. In this study, radio refractive index and modified refractivity gradient were computed using the results of measurements of atmospheric pressure, temperature and relative humidity made in Akure (7.15^°N, 5.12^°E), South Western Nigeria using Davis 6162 Wireless Vantage Pro2 weather stations (Integrated Sensor Suite, ISS) positioned at five different height levels beginning from the ground surface and at intervals of 50 m from the ground to a height of 200 m on a tower/mast owned by the Nigeria Television Authority (NTA) located at Iju in Akure north local government area of Ondo state but which is no longer being used. The study utilized one year of data measured between January and December 2008. From the results, the modified refractivity was calculated and found to increase with increasing altitude. The values were observed to be generally high during the rainy periods and generally low during the dry periods. The study also revealed that for microwave propagation in this geographic zone, the propagation condition is mostly super-refractive.     

Der Brechungsindexgradient für elektromagnetische Wellen (Cm-bis M-Band) in der maritimen Grenzschicht der Atmosphäre

Zusammenfassung Für ein in der Abhandlung von K. Brocks [1955] abgeleitetes Verfahren der Berechnung von Brechungsindex-Profilen unmittelbar über dem Meer werden weitere Hilfsmittel angegeben, insbesondere eine graphische Psychrometertafel (Tafel 8), aus der der Dampfdruck der Luft [in mb] als Funktion der Temperatur des feuchten und trockenen Thermometers entnommen werden kann, und ein Diagramm des Wasserdampfdrucks und des Sättigungsdampfdruckes der Luft sowie der relativen Luftfeuchtigkeit als Funktion der Lufttemperatur (Tafel 9).Es wird ferner ein Kurzverfahren mitgeteilt, das eine schnelle Berechnung des Brechungsindexprofils über dem Meer ermöglicht aus Messungen der Lufttemperatur, Luftfeuchtigkeit, Windgeschwindigkeit und Wassertemperatur. Hierfür wird ein Diagramm gegeben (Tafel 10), das den BrechungswertN=(n–1) 10^–6 als Funktion der Temperatur des trockenen und des feuchten Thermometers bzw. der Wassertemperatur enthält.

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On the gradient of the refractive index of electro-magnetic waves (centimetre-to metre-waves) in the maritime boundary layer of the atmosphere. 2^nd article

Summary The present paper adds further aids to the method developed by K. Brocks [1955] for the computation of the curves of the refractive index occurring immediately above the sea surface. These aids, before all, consist in a graphical psychrometer plate (plate 8) and a diagramme (plate 9). Plate 8 permits to derive from it the vapour pressure of the air [in mb] as a function of temperature to be read from dry bulb and a wet bulb thermometres. Plate 9 represents the water vapour pressure and the saturation pressure of the air as well as relative humidity of the air as a function of air temperature.Besides, an abbreviated method is discussed permitting a time-saving computation of the curves of the refractive index above sea surface from measurements of air temperature, atmospheric moisture, wind velocity, and water temperature. This computation is carried out with the aid of a diagram (plate 10), giving the refractive valueN=(n–1) 10^–6 as a function of the temperature, measured with a dry bulb and a wet bulb thermometre, or as a function of the water temperature, respectively.

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Sur le gradient de l'indice de réfraction des ondes électromagnétiques (de 0,1 m à 1m), présentes dans la couche limite maritime de l'atmosphère. 2^e article

Résumé Le travail actuel ajoute à la méthode développée par K. Brocks [1955] d'autres moyens pour le calcul des courbures du gradient de l'indice de réfraction se présentant immédiatement au-dessus de la surface de la mer. Ces moyens se composent surtout d'une représentation graphique des valeurs psychométriques (planche 8) et d'un diagramme (planche 9). La planche 8 permet d'en tirer la pression de vapeur de l'air [en mb] en fonction de températures indiquées sur de thermomètres mouillés ou sur de thermomètres secs. La planche 9 montre la pression de vapeur d'eau et la tension de vapeur saturante de l'air ainsi que l'humidité relative de l'air en fonction de la température de l'air.De plus, une méthode abbréviée est présentée qui permet de calculer, sans perdre beaucoup de temps, au moyen des mesures de la température de l'air et de l'eau, de l'humidité de l'air et de la vitesse du vent, la courbure de l'indice de réfraction au-dessus de la mer. Ce calcul se fait à l'aide d'un diagramme (planche 10) qui donne la valeur de réfractionN=(n}-1) 10^–6 en fonction de la température du thermomètre sec et du thermomètre mouillé ou la représente respectivement en fonction de la température de l'eau.

     

Tidal currents and residual currents at Norderney,Elbe 1, and Aussen-Eider lightships and their variation under the influence of prevailing winds

Summary Four hourly current-and wind observations during the years 1924–1927 at the German lightvessels Norderney, Elbe 1, and Aussen-Eider were subjected to harmonic analysis with emphasis on the influence of the wind on the residual as well as on the tidal current. The tidal current is strongest at Elbe 1 and weakest at Aussen-Eider. The half-monthly inequality of the current is strongly influenced by a ₂ tidal component. Wind influences the velocity, phase and duration of ebb-and flow current in a systematic way at Norderney and Elbe 1. Deviations from the mean tidal current are caused mainly by the change in wind direction rather than by wind velocity. The mean residual current is weak at the three stations. But wind driven currents have a velocity up to 5 times as great as the mean residual current and reverse their direction with the wind. The annual variation of the mean residual current, however, is caused only to a small part by the annual wind variation.Abbreviations used in this paper Gr. M. Tr. Greenwich moon transit, i.e. Greenwich civil time of the upper or lower transit of the moon through the meridian of Greenwich - C _n computed tidal current at M1/2Hn - C _n ^m computed mean tidal current at M1/2Hn - M _n Moon-half hour mean, i.e. mean of all current velocities observed during M1/2Hn - M.A. Moon age of an observation, true Greenwich time of Gr.M.Tr. directly preceeding the time of observation, expressed in 12 integral numbers, each representing M.A. falling in 12 different hourly intervals - M1/2H Moon-half hour, 1/2 of the interval between one moon transit and the next, i.e. 1/24 of 12h25m - R _n ^o ,R _n ^' ,R _n ^" residual current computed by harmonic analysis ofn M1/2H means of the mean current, the current at weak winds, and the current at strong winds respectively - d.o.f. degrees of freedom - standard deviation ofC _n fromM _n - ^* mean standard deviation ofC _n fromM _n for analysis with weighted means - A _o Standard error of the residual currentA _o - AB standard error of the harmonic coefficientsA ₁,B ₁,A ₂,B ₂,... - S ₂ Phase of the current componentS ₂     

Biodegradability and Toxicity of Anionic Surfactants

Alkyl sulphates of the general formula CH_{2n + 1}-O-SO₃Na and alkyl sulphonates of the general formula C_nH_{2n + 1}-SO₃Na, where n = 8, 10, 12, 14 in each series have been tested for biodegradability with the modified OECD screening test No. 301 E, and for toxicity with Daphnia magna and with Photobacterium phosphoreum (the Microtox^TM test). The results show that both alkyl sulphates and alkyl sulphonates are biodegraded with the alkyl sulphates degrading more rapidly under the test conditions. The alkyl sulphates also have higher toxicity to both test species and for both alkyl sulphates and sulphonates the toxicity increases linearly with increasing molecular weight of the surfactant.     

On the variation of temperature structure parameter in cloud- and clear-air during the summer monsoon season

High resolution aicraft observations of temperature were made in cloud-air and clear-air at different heights in the lower atmosphere over the Deccan Plateu, India, during the summer monsoon season (June–September) of 1976. Temperature fluctuations in the horizontal at each flight level were utilised for computing the temperature structure parameter (C _T ² ) at that level for studying the hieght dependence ofC _T ² . The results were found to be in agreement with those obtained by other investigators. Also, the height variations ofC _T ² in cloud-air and clear-air during active and weak monsoon conditions are studied. Marked differences were noticed in the behaviour ofC _T ² during active and weak monsoon conditions.     

Identification of marine natural gases with different origin sources

Kinetic experiments of gas generation for typical samples of marine gas precursors including low-maturity kerogen, residual kerogen and oil as well as dispersed liquid hydrocarbon (DLH) in source rocks were performed by closed system, and the evolution trends of molecular and isotopic compositions of natural gases from different precursors against the maturity (R ₀%) at laboratory conditions were analyzed. Several diagrams of gas origin were calibrated by using the experimental data. A diagram based on the ratio of normal and isomerous butane and pentane (i/nC₄ ? i/nC₅) was proposed and used to identify the origins of the typical marine natural gases in the Sichuan Basin and the Tarim Basin, China. And the maturities of natural gases were estimated by using the statistical relationships between the gaseous molecular carbon isotopic data and maturities (δ¹³C-R ₀%) with different origins. The results indicate that the molecular and isotopic compositions of simulated gases from different precursors are different from each other. For example, the dryness index of the oil-cracking gas is the lowest; the dryness indices of gases from DLH and kerogen in closed system are almost the same; and the dryness index of gases from residual kerogen is extremely high, indicating that the kerogen gases are very dry; the contents of non-hydrocarbon gases in kerogen-cracking gases are far higher than those in oil-cracking and DLH-cracking gases. The molecular carbon isotopes of oil-cracking gases are the lightest, those of kerogen in closed system and GLH-cracking gases are the second lightest, and those of cracking gases from residual kerogen are the heaviest. The calibration results indicate that the diagrams of In(C₁/C₂)-In(C₂/C₃) and δ^{4 3}C₂-δ^{4 3}C₃-In(C₂/C₃) can discriminate primary and secondary cracking gases, but cannot be used to identify gas origin sources, while the diagram of i/nC₄ ? i/nC₅ can differentiate the gases from different precursors. The application results of these diagrams show that gas mixtures extensively exist in China, which involved the gases from multiple precursors and those from different maturity stages. For example, marine gases in the Sichuan Basin involve the mixture of oil-cracking gases and high-over-maturated kerogen gases, while those in the Tarim Basin involve not only the mixture of gases from multiple precursors, but also those from different maturity gases and post-reservoir alternations such as oxidized degradation and gas intrusion processes.     

FUNDAMENTAL FUNCTIONS FOR HORIZONTALLY STRATIFIED EARTH*

The potential distribution and the wave propagation in a horizontally stratified earth is considered and the analogy of the mathematical expression for seismic transfer function, electromagnetic and electric kernel functions, and magnetotelluric input impedance is discussed. Although these specific functions are conveniently treated by a separate expression in each method, it is indicated that the function for seismic and electromagnetic methods is mathematically the same with a change in the physical meaning of the variables from one method to the other. Similarly, the identity of the mathematical expressions of the resistivity kernel function and magnetotelluric input impedance is noticed. In each method a specific geophysical function depends on the thickness and the physical properties of the various layers. Every specific function involves two interdependent fundamental functions, that is P_n and Q_n, or P_n and P*_n, having different physical meaning for different methods. Specific functions are expressible as a ratio P_n/Q_n or P*_n/P_n. Fundamental functions may be reduced to polynomials. The fundamental polynomials Q*_n and P*_n describing the horizontally stratified media are a system of polynomials orthogonal on the unit circle, of first and second order, respectively. The interpretation of geophysical problems corresponds to the identification of the parameters of a system of fundamental orthogonal polynomials. The theorems of orthogonal polynomials are applied to the solution of identification problems. A formula for calculating theoretical curves and direct resistivity interpretation is proposed for the case of arbitrary resistivity of the substratum. The basic equation for synthetic seismograms is reformulated in appendix A. In appendix B a method is indicated for the conversion of the seismic transfer function from arbitrary to perfectly reflective substratum.     

Catchment environmental change over the 20th Century recorded by sedimentary leaf wax n-alkane δ~(13)C off the Pearl River estuary

The compound-specific stable carbon isotope compositions(δ~(13)C) of leaf wax n-alkanes from two short sediment cores recovered off the Pearl River estuary(PRE) were analyzed to check for their capability of indicating decadal scale catchment environmental change. Sedimentary long-chain n-alkanes exhibited an odd-over-even predominance, with a maximum at n-C_(29) or n-C_(31), indicating their leaf wax origin was from vascular plants. The δ~(13)C values of C_(29) and C_(31) n-alkane in all the sediment samples were in the range of -28.8‰ to -31.2‰, consistent with the C_3 plant-dominated vegetation in the Pearl River catchments. The time series of δ~(13)C records from the two cores were comparable and displayed a decreasing trend from the early 20 th century to the end of the 1970s, followed by a reversal in that change leading to continued increase for ca. 15 years. After being corrected for the effect of atmospheric CO_2 rise and δ~(13)C_(atm) decline, the δ~(13)C_(29) records largely retained their raw changing pattern; the post-1980 increase being more conspicuous. The slightly decreasing trend in corrected δ~(13)C records before around 1980 may have been caused by an increase in precipitation, whereas the subsequent increase of δ~(13)C is likely associated with the observed dry climate and/or intensive anthropogenic deforestation. Our results thus demonstrate that leaf wax n-alkanes buried in the sediments off the PRE may well reflect change in the regional climate and/or human activity in the river catchments over the past century.     

Preliminary study on the source field mode of geomagnetic six-month-period variations

The monthly means of north component X of geomagnetic field from 16 observatories during 1984–1988 were analyzed using the Sompi spectral analysis technique Most of these observatories are located in China. The analysis of the semiannual variations indicates that the latitude has no apparent effect on the X component. This clearly implies that the source field mode of semiannual variations cannot simply be described by using the p ₁ ⁰ mode. Using the p ₁ ⁰ mode to estimate the inductive scale lengthC in the semiannual period, the value ofC at each observatory would be biased significantly. The purpose of this study is to find which kind of modes is optimal for estimating the values ofC corresponding to the semiannual variations. The results show that a composite mode, involving five terms P _n ⁰ (n = 1,, 5), might be a reasonable and acceptable one     

Inversion of gravity and magnetic anomalies over some bodies of simple geometric shape

The general expression for gravity and magnetic anomalies over thin sheets and sloping contacts may be expressed as a polynomial of the formFx ²+C₁Fx+C₂F+C₃x³+C₄x²+C₅x+C₆. The initial parameters of the source are obtained from the coefficientsC ₁, C₂,..., C₆ which may be solved by inverting a 6×6 matrix. The initial parameters are modified by successive iteration process using the difference formula until the root mean square error between the observed and calculated anomalies is a minimum. The regional background which may be in the form of a polynomial is estimated by the computer itself. This method is applied on a number of field anomalies and is found to yield reliable estimates of depth and other parameters of the source.     

Carbon and water cycling in a Bornean tropical rainforest under current and future climate scenarios

We examined how the projected increase in atmospheric CO₂ and concomitant shifts in air temperature and precipitation affect water and carbon fluxes in an Asian tropical rainforest, using a combination of field measurements, simplified hydrological and carbon models, and Global Climate Model (GCM) projections. The model links the canopy photosynthetic flux with transpiration via a bulk canopy conductance and semi-empirical models of intercellular CO₂ concentration, with the transpiration rate determined from a hydrologic balance model. The primary forcing to the hydrologic model are current and projected rainfall statistics. A main novelty in this analysis is that the effect of increased air temperature on vapor pressure deficit (D) and the effects of shifts in precipitation statistics on net radiation are explicitly considered. The model is validated against field measurements conducted in a tropical rainforest in Sarawak, Malaysia under current climate conditions. On the basis of this model and projected shifts in climatic statistics by GCM, we compute the probability distribution of soil moisture and other hydrologic fluxes. Regardless of projected and computed shifts in soil moisture, radiation and mean air temperature, transpiration was not appreciably altered. Despite increases in atmospheric CO₂ concentration (C_a) and unchanged transpiration, canopy photosynthesis does not significantly increase if C_i/C_a is assumed constant independent of D (where C_i is the bulk canopy intercellular CO₂ concentration). However, photosynthesis increased by a factor of 1.5 if C_i/C_a decreased linearly with D as derived from Leuning stomatal conductance formulation [R. Leuning. Plant Cell Environ 1995;18:339–55]. How elevated atmospheric CO₂ alters the relationship between C_i/C_a and D needs to be further investigated under elevated atmospheric CO₂ given its consequence on photosynthesis (and concomitant carbon sink) projections.     

Characterization of the negative carbon isotope shift in segment C2, its global implications as a harbinger of OAE1a

Lower Cretaceous C-isotope records show intermittent negative/positive spikes, and consistent patterns of coeval chemostratigraphic curves thus document shifts that signal simultaneous responses of temporal changes in the global carbon reservoir. The standard pattern registered by the δ ¹³C_org and δ ¹³C_carb in Lower Aptian sediments includes distinct isotope segments C1 to C8 (Menegatti et al., 1998). In the El Pui section, Organyà Basin, Spain, C-isotope segment C2 is the longest interval preceding segments C3–C6 associated with oceanic anoxic event 1a (OAE 1a), and reveals a distinct negative shift of ~1.8‰ to ~2.23‰ defining the C-isotope pattern within that interval. Total inorganic carbon (TIC), total organic carbon (TOC), δ ¹³C_org, microfacies, n-alkanes show no difference before, during, or after the negative inflection. The biomarkers indicate that organic matter (OM) mainly originates from algal/microbial sources because short-chain length homologues (≤nC₁₉) dominate. nC₂₀ through nC₂₅ indicate some contribution from aquatic vegetation, but little from higher plants (>nC₂₅), as also suggested by the terrestrial/aquatic ratio of n-alkanes or (TAR) = [(nC₂₇+nC₂₉+nC₃₁)/(nC₁₅+nC₁₇+nC₁₉)] (averages 0.085). We suggest that conjoint pulses of contemporaneous LIPs (Ontong Java) and massive explosive volcanism in northeast Asia, the Songliao Basin (SB-V), best conform to plausible causes of the negative intra-C2 carbon isotopic excursion (CIE) at that time. Because of its apparent common occurrence the intra-C2 inflection could be a useful marker harbinger to the more pronounced CIE C3, the hallmark of OAE1a.     

Day-time variations of the equivalent electron concentration in the non-sounded lower ionosphere

Summary Based on data on the lowest reflected frequencyf _min and on information on the lower and upper boundaries of the non-sounded lower ionosphere, an equivalent electron concentration for all concentrations below the correspondingf _min was determined. Day-time variations of the equivalent concentration are investigated, confirming that there is a cosine relation to the solar zenith angle. The power index of that relation has an outlined seasonal course with a maximum in April and October, while the absolute seasonal minimum is during the winter (the summer minimum is slightly outlined). The mean yearly values of the index are almost constant:n _N 0.5 for solaractivity,I ₁₅₀₀ to 115.10^–22 W Hz^–1 m². During higher activityn _N changes correspondingly toI ₁₅₀₀ according to relation (12). The variations ofn _N during high solar activity show that the altitude gradient and temperature gradient in the low ionosphere are becoming proportional toI ₁₅₀₀ when the solar x-ray radiation exceeds a certain level. The results obtained confirm the reliability of the method developed for employingf _min in aeronomic investigations.     

Echo intensity data as a directional antenna for observing processes above sloping ocean bottoms

Relative ‘echo intensity’ data (dI) from a bottom-mounted four-beam 300 kHz acoustic Doppler current profiler (ADCP) are used to infer propagation of vigorous processes above a continental slope. The 3- to 60-m horizontal beam spread and the 2-Hz sampling allow the distinction of different arrival times t _i , i = 1,..., 4, at different distances in the acoustic beams from sharp changes in dI-content associated with frontal non-linear and turbulent bores or ‘waves’. The changes in dI are partially due to variations in amounts of resuspended material carried by the near-bottom turbulence and partially due to the fast variations in density stratification (‘stratified turbulence’), as inferred from 1-Hz sampled thermistor string data above the ADCP. Such bores are observed to pass the mooring up to 80 m above the bottom, having typical propagation speeds c = 0.15–0.5 m s⁻¹, as determined from dI(t _i ). Particle speeds in the immediate environment of a bore amount to |u|_env=c ± 0.05 m s⁻¹, the equality being a necessary condition for kinematic instability, whilst the maximum particle speeds amount |u|_max = 1.2–2c. The dI-determined directions of up-, down- and alongslope processes are all to within ±10° of the ADCP’s beam-spread averaged current (particle velocity) data.     

Genetic features of gas-condensate reservoirs in the Kekeya Field,southwest depression in the Tarim Basin,China

Oils, condensates and natural gases in the Kekeya Field, southeast depression of the Tarim Basin were studied for their geochemical characteristics. According to the distribution analysis of the C₂/C₃ values with C₁/C₂ values, C₂/C₃ values with C₁/C₃ values, as well as C₂/C₃ values with dryness index, there are two different types of natural gases in the studied field, which are spatially regularly distributed. One is the oil cracking gas, located on shallow reservoirs over X ₅ ² reservoir, namely Upper oil legs; the other is kerogen cracking gas, located on X ₇ ² reservoirs, X₈ reservoirs and E₂ k reservoirs, namely Lower oil legs. In addition, the distribution patterns of molar concentration of oils and condensates with different carbon numbers of the n-alkanes in the Kekeya Field indicate that the crude oils have experienced several kinds of secondary alterations, which were closely related to the charging of gaseous hydrocarbons after petroleum accumulation. These results indicate that, based on the research of δ ¹³C values of individual hydrocarbons, heptane values and isoheptane values of light hydrocarbons and aromatic maturity parameters for oils, condensates and natural gases, oils and gases were charged at different geological time in the Kekeya Field.