Late Silurian–Middle Devonian long-term shoreline shifts on the northern Gondwanan margin: eustatic versus tectonic controls     

Dmitry A. Ruban  Clinton P. Conrad 《Proceedings of the Geologists' Association. Geologists' Association》2013

Long-term shoreline shifts reflect eustatic changes, tectonic activity, and sediment supply. Available lithostratigraphical data from northern Africa, Arabia, and the Tethys Hymalaya, coupled with facies interpretations, permit us to trace late Silurian–Middle Devonian long-term shoreline shifts across the northern Gondwanan margin and to compare them with constraints on global sea-level changes. Our analysis establishes a regression–transgression cycle. Its coincident global sea-level changes reveal the dominance of the eustatic control. A transgression–regression cycle observed in Arabia is best explained by regional subsidence. Our study highlights the importance of constraining the role of regional tectonics when interpreting shoreline shifts.  相似文献   

三角形形状因子对地壳形变计算精度的影响   总被引：11，自引：5，他引：6  

伍吉仓  邓康伟  陈永奇 《大地测量与地球动力学》2003,23(3):26-30

引入三角形内切圆半径与外接圆半径之比值作为三角形形状因子，讨论利用三角形法计算应变分量的精度与三角形形状因子之间的关系。设计一种涵盖所有三角形形状的方法，计算分析了用三角形法计算应变分量精度的分布。研究表明：当三角形形状因子达到0．36时，计算得到的应变分量均方差，一般不会超过位移数据均方差的3倍；而当三角形形状因子小于0．1时，计算得到的应变分量均方差会陡然增大，这样的三角形一般不适合用于应变分量的计算。在利用GPS观测站组成三角形计算地应变时，建议所组成的三角形形状因子的阈值应取为0．1～0．36。  相似文献   

The Influence of Benthic Macrofauna on the Erodibility of Intertidal Sediments with Varying mud Content in Three New Zealand Estuaries     

Rachel J. Harris  Conrad A. Pilditch  Barry L. Greenfield  Vicki Moon  Ingrid Kröncke 《Estuaries and Coasts》2016,39(3):815-828

Fine sediment inputs can alter estuarine ecosystem structure and function. However, natural variations in the processes that regulate sediment transport make it difficult to predict their fate. In this study, sediments were sampled at different times (2011–2012) from 45 points across intertidal sandflat transects in three New Zealand estuaries (Whitford, Whangamata, and Kawhia) encompassing a wide range in mud (≤63 μm) content (0–56 %) and macrofaunal community structure. Using a core-based erosion measurement device (EROMES), we calculated three distinct measures of sediment erosion potential: erosion threshold (? _c ; N m^?2), erosion rate (ER; g m^?2 s^?1), and change in erosion rate with increasing bed shear stress (m _e ; g N^?1 s^?1). Collectively, these measures characterized surface (? _c and ER) and sub-surface (m _e ) erosion. Benthic macrofauna were grouped by functional traits (size and motility) and data pooled across estuaries to determine relationships between abiotic (mud content, mean grain size) and biotic (benthic macrofauna, microbial biomass) variables and erosion measures. Results indicated that small bioturbating macrofauna (predominantly freely motile species <5 mm in size) destabilized surface sediments, explaining 23 % of the variation in ? _c (p ≤ 0.01) and 59 % of the variation in ER (p ≤ 0.01). Alternatively, mud content and mean grain size cumulatively explained 61 % of the variation in m _e (p ≤ 0.01), where increasing mud and grain size stabilized sub-surface sediments. These results highlight that the importance of biotic and abiotic predictors vary with erosion stage and that functional group classifications are a useful way to determine the impact of benthic macrofauna on sediment erodibility across communities with different species composition.  相似文献   

Fluids during diagenesis and sulfate vein formation in sediments at Gale crater,Mars          下载免费PDF全文

S. P. Schwenzer  J. C. Bridges  R. C. Wiens  P. G. Conrad  S. P. Kelley  R. Leveille  N. Mangold  J. Martín‐Torres  A. McAdam  H. Newsom  M. P. Zorzano  W. Rapin  J. Spray  A. H. Treiman  F. Westall  A. G. Fairén  P.‐Y. Meslin 《Meteoritics & planetary science》2016,51(11):2175-2202

We model the fluids involved in the alteration processes recorded in the Sheepbed Member mudstones of Yellowknife Bay (YKB), Gale crater, Mars, as revealed by the Mars Science Laboratory Curiosity rover investigations. We compare the Gale crater waters with fluids modeled for shergottites, nakhlites, and the ancient meteorite ALH 84001, as well as rocks analyzed by the Mars Exploration rovers, and with terrestrial ground and surface waters. The aqueous solution present during sediment alteration associated with phyllosilicate formation at Gale was high in Na, K, and Si; had low Mg, Fe, and Al concentrations—relative to terrestrial groundwaters such as the Deccan Traps and other modeled Mars fluids; and had near neutral to alkaline pH. Ca and S species were present in the 10^?3 to 10^?2 concentration range. A fluid local to Gale crater strata produced the alteration products observed by Curiosity and subsequent evaporation of this groundwater‐type fluid formed impure sulfate‐ and silica‐rich deposits—veins or horizons. In a second, separate stage of alteration, partial dissolution of this sulfate‐rich layer in Yellowknife Bay, or beyond, led to the pure sulfate veins observed in YKB. This scenario is analogous to similar processes identified at a terrestrial site in Triassic sediments with gypsum veins of the Mercia Mudstone Group in Watchet Bay, UK.  相似文献   

On thermal springs a contribution to the knowledge of their nature     

V. Conrad 《Meteorology and Atmospheric Physics》1956,9(3):371-405

Summary Temperature and discharge of fourteen thermal spring at Badgastein (Hohe Tauern, Austrian Alps) were observed throughout a year.Daily observations were made at four springs. With these an obviously rapid increase in temperature of 1 Cdeg occurred from May 11 to May, 12 1931. Generally, short variations are exceedingly small. Six other springs, observed once a week, showed an increase in temperature of an equal amount. Synchronism of the increase among all the ten springs could be made plausible. The dropping back of temperature on May 23 occurred unequivocally simultaneously with all the ten springs.The curve ofdischarge remained, however, fully undisturbed within the time of the temperature discountinuity.From the synchronism of the disturbance of temperature the conclusion was drawn thatall the ten springs may originate from one and the same source in the interior of the mountains.The main problem that should be cleared up in this study on temperature and discharge is the question how far the spring water is either juvenile or vadose (atmospheric) or mixed of both.An investigation into the variability of temperature and discharge was the first step. The daily observations of four springs offered a convenient material. The absolute variability (A. V.) (Table 5, last line) is extremely small, 0.045 Cdeg, on the average, for the four springs. As a supplement theinterdiurnal variability (I. V.) was calculated. On the average, this is still smaller than the regular average variability. It is 0.026 Cdeg. A comparison of the magnitude of R. V.^* and R. I. V.^* of discharge for December, January and July, August arrived partly at contradictory indications. The differences, however, between the two seasons are of an order of magnitude of only hundredth per cent so that the idea is at hand to think of an effect caused by chance.The further investigation leads to the conclusion that some of the springs are likely of juvenile nature and perhaps sometimes mixed withnon-essential amounts of atmospheric water.Rain water penetrating the clefts has either no influence on the temperature or it must have a cooling effect. The discharge must increase in any case if rain water is penetrating. The number of coolings from day to day must beincreased then in thewarm half-year and just so the number of cases withdischarge increasing from day to day. These effects are examined by means of two methods. In some cases the statistical indications were qualitatively again in favor of the assumption that rain water penetrates in small amounts. The magnitude of the differences is, however, not large enough, and the agreement of the behavior of the single springs not sufficient to exclude the role ofchance. Also this investigation arrived, at the result that one or the other indication speaks for the assumption that occasionally after copious rainfalls insignificant amounts of atmospheric water are mixed with the thermal water.Especially in consideration of the reslts of the first section that some of the springs carryessentially juvenile water one could think of anything but of variations of temperature and discharge in the length of a year.Figures 4a and 4b, however, show examples of such, at least fictive, annual variations. With the one spring, variations of temperature and discharge are parallel to one another; in the other spring the variations are opposite to one another; with a spring, the water of which is mixed of juvenile water with greater amounts of atmospheric water, the opposite type must be expected with minimum of temperature and maximum of discharge in summer. Only one of the fourteen springs (W) fulfils these conditions.The reality of the annual variations is dubious since with most important spring groups the ranges of both elements are very small. A method given by the present author permits estimating the reality of an annual variation so far as only practicallywhole-year sine-waves are considered.The main results is that four springs of the fourteen show areal annual variation of temperature and at the same time of discharge.Only a clue can be given to a possibly correct explanation. Themovement of the poles showstwo andonly two periodical components that cause certain stresses in the crust of the earth. With a probability not too small these stresses contribute to the release of earthquakes and could also influence the mechanism of the springs. The one component has a wave length of 12 months, the other one of 14 months. If it would be possible to discover the second 14-months-variation of temperature and discharge from a new material of a few years the enigma of the annual variation, otherwiseununderstandable, could be solved to a certain degree.In the last section some numerical characteristics of the springs appear. Statistics show that a real annual variation of temperature is found only in springs of a medium temperature and not in the warmest and coolest springs.All of the methods applied here, lead to the conclusion thatsome of the springs at Badgastein carry generally pure juvenile water possibly mixed some-times with negligible amounts of vadose water.

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Zusammenfassung Temperatur und Ergiebigkeit von 14 Thermalquellen in Badgastein (Hohe Tauern, Österreich. Alpen) wurden ein Jahr hindurch beobachtet. Bei vier Quellen erfolgten die Messungen täglich. Bei diesen wurde ein offenbar rascher Anstieg um zirka 1° C vom 11. bis 12. Mai beobachtet, während sonst die kurzen Schwankungen ausnehmend klein sind. Bei sechs weiteren Quellen, bei denen nur einmal in der Woche gemessenAls Hauptresultat wird festgestellt, daß vier Quellenreale Jahresschwankung von Temperatur sowohl als von Ergiebigkeit aufweisen. Zur Erklärung ist daran zu erinnern, daß dieBewegung der Erdpole zwei und nur zwei periodische Komponenten aufweist, die gewisse Spannungen in der Erdkruste erzeugen müssen. Diese tragen z. B. mit nicht unbedeutender Wahrscheinlichkeit zur Auslösung von Erdbeben bei und könnten so auch den Quellmechanismus beeinflussen. Die eine Komponente hat eine Wellenlänge von 12 Monaten, die andere eine von 14 Monaten. Wenn es gelänge, auch diese 14monatige Schwankung von Temperatur und Ergiebigkeit der Quellen in einem mehrjährigen Material festzustellen, wäre wohl das Rätsel der sonst unverständlichen Jahresschwankung gelöst.Im letzten Abschnitt erscheinen einige numerische Charakteristiken der Quellen. Unter anderem ist zu ersehen, daß weder die wärmsten noch die kühlsten Quellen dem besprochenen Jahresgang unterworfen sind, sondern nur solche, die einer mittleren Temperaturgruppe angehören.Alle hier angeführten Untersuchungsmethoden führen zu dem Schlusse, daß dasjuvenile Wasser einiger der Gasteiner Quellen nur mit unwesentlichen Teilen atmosphärischen Wassers vermischt sein kann.

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Résumé On a observé pendant une année la température et le débit de 14 sources thermales à Bad Gastein (Hohe Tauern, Alpes autrichiennes). Pour 4 sources on fit des mesures quotidiennes, pour 6 autres une fois par semaine et pour les 4 dernières une fois en 5 semaines. Une hausse remarquable de température de 1° s'est produite pour toutes les sources au milieu de mai, tandis que le débit restait inchangé. On en conclut que les sources ont une origine commune à l'intérieur de la montagne.Le problème principal est celui de savoir si les eaux de ces sources sont d'origine atmosphérique ou non. A cet effet on a examiné la variabilité de la température qui est en moyenne extrêmement faible, de l'ordre de 0,045°; la variation interdiurne est encore plus petite: 0,026°. En ce qui concerne le débit, la variabilité relative de quatre sources n'atteint pas 0,5%. On est amené à conclure que quelques-unes des sources ne reçoivent pas d'apport d'eau météorique. Si de l'eau de pluie pénètre dans le sous-sol, elle doit ou bien ne pas modifier la température des sources ou alors l'abaisser; elle doit parallèlement accroître le débit. L'étude statistique montre que tout au plus certaines fortes chutes de pluie peuvent se mêler partiellement à l'eau des cources.Ces résultats font douter d'une variation de température et de débit à période annuelle. Quatre sources présentent cependant une variation annuelle des deux grandeurs, faible il est vrai. Il est possible que l'explication puisse en être trouvée un jour dans le déplacement du pôle, capable de provoquer des tensions de la croûte terrestre et qui ne présente que deux périodes de 12 et de 14 mois. Il faut cependant remarquer que les sources les plus chaudes et les plus froides ne présentent pas cette variation annuelle. Les constatations faites pour les sources de Gastein pourraient aussi être valables pour d'autres sources soumises à des conditions géologiques semblables. wurde, trat gleich großer Anstieg ein. Gleichzeitigkeit desselben mit dem der vier täglich beobachteten Quellen konnte plausibel gemacht werden. Bei dem Zurückfallen der Temperatur am 23. Mai unterliegt die Gleichzeitigkeit bei allen 10 Quellen keinem Zweifel. Die Kurve der Ergiebigkeit der 10 Quellen verläuft merkwürdigerweise völlig ungestört. Aus dem Synchronismus der Störung wird geschlossen, daß alle zehn Quellen wahrscheinlich einen gemeinsamen Ursprung im Innern des Gebirges haben.Das Hauptproblem, zu dessen Klärung eine Untersuchung der Temperatur und Ergiebigkeit beitragen soll, liegt in der Frage, wieweit das Quellwasser atmosphärischen (vadosen) oder juvenilen Ursprungs ist. Zu diesem Zwecke wurde eine Untersuchung der Veränderlichkeit der beiden Elemente an Hand der täglichen Beobachtungen an vier Quellen durchgeführt. Die mittlere absolute Veränderlichkeit (Tabelle 5, letzte Zeile) ist ausnehmend klein und beträgt im Mittel der vier Quellen 0,045° C; die interdiurne Veränderlichkeit (I. V.) ist im Mittel noch kleiner als die mittlere Veränderlichkeit und beträgt 0,026°C.Für die Untersuchung derErgiebigkeit wurde dierelative Veränderlichkeit (R. V.) angewendet; sie erreicht im Mittel der vier Quellen nicht 1/2%, die R. I. V. nicht einmal 0,4%.Ein Vergleich der Größen von R. V. und R. I. V. für Dezember (Januar und Juli) August führt zu teilweisem Widerspruch. Die Unterschiede zwischen den beiden Jahreszeiten bewegen sich jedoch nur in hunderstel Prozent. so daß es naheliegt, an eine Zufallswirkung zu denken. Die weitere Untersuchung führt dann zu dem Schluß, daßeinige von den untersuchten Quellen keinen wesentlichen Zusatz von atmosphärischem Wasser erhalten.Wenn Regenwasser die Klüfte durchdringt, hat es entweder keinen Einfluß auf die Temperatur oder es müßte abkühlend wirken. Die Ergiebigkeit muß bei zugesetztem Regenwasser jedenfalls ansteigen. Wenn also Außenwasser eindringt muß die Zahl der Abkühlungen von Tag zu Tag im warmen Halbjahr steigen und ebenso die der zunehmenden Ergiebigkeit. Diese Effekte werden mittels zweier Methoden geprüft. Als Resultat ergab sich wieder, daß die Statistiken in manchen Fällenqualitativ für die Annahme von eindringendem Regenwasser sprechen, daß aber diequantitativen Unterschiede nicht groß genug sind, das Verhalten der einzelnen Quellen nicht einheitlich genug, um das Wirken des Zufalls auszuschließen. Auch diese Untersuchung kommt zum Schluß, daß wohl das eine oder andere Anzeichen dafür spricht, daß gelegentlich größerer Regenfälle kleine Mengen atmosphärischen Wassers dem Quellwasser beigemengt werden.Speziell mit Rücksicht auf die Feststellung, daß die Quellen wesentlich juveniles Wasser aus den Tiefen der Gebirgskette zutage führen, sollte man alles eher als Schwankungen mit Jahresperiode von Temperatur und Ergiebigkeit vermuten. Fig. 4 und 5 zeigen Beispiele solcher, mindestens fiktiver Jahresgänge und auch die extremen Möglichkeiten. Bei der einen Quelle variieren Temperatur und Ergiebigkeit gleichsinnig, bei einer zweiten spiegelbildlich. Bei einer reichlich mit atmosphärischem Wasser gemischten Quelle müßte spiegelbildliches Verhalten auftreten, mit Temperaturminimum und Ergiebigkeitsmaximum im Sommer. Nur eine einzige Quelle (W) erfüllt diese Bedingung. Was die Realität der sich ergebenden Jahresschwankung so fraglich macht, sind die bei den wichtigsten Quellgruppen auftretenden, sehr kleinen Schwankungsweiten. Eine vom Verfasser gegebene Methode erlaubt es, die Realität einer Jahresschwankung abzuschätzen, soweit man es mit einer praktisch ganzjährigen Sinuswelle zu tun hat.

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With 5 Figures  相似文献   

Tertiary and quaternary geodynamics of southern Lut (Iran) as deduced from palaeomagnetic, isotopic and structural data     

G. Conrad  R. Montigny  R. Thuizat  M. Westphal 《Tectonophysics》1981,75(3-4)

Palaeomagnetic measurements and K---Ar age determinations carried out on lavas from Dash-e-Lut in southeast Iran reveal an anticlockwise rotation of about 90° of the depression south of Lut between Paleocene and Miocene time. It is probably associated with the collision between India and Asia.  相似文献   

Quantitative analysis of top-seal capacity: offshore Netherlands,southern North Sea     

Spain  David R.  Conrad  Curtis P. 《Geologie en Mijnbouw》1997,76(3):217-226

Sealing characteristics of the caprock to the Main Buntsandstein reservoir sands in the P blocks in the Dutch offshore are assessed based on a core from the P15 well. The core which represents the Main Buntsandstein, Solling, Röt, and Muschelkalk interval has been analyzed using standard geologic and petrophysical techniques including mercury-injection capillary-pressure tests. The caprock to the Main Buntsandstein reservoir sands consists of anhydritic and/or dolomitic sandstone to argillaceous siltstone, silty shale, and dolostone. Early emplacement of nodular anhydrite followed by cementation and replacement by anhydrite, dolomite, and siderite has resulted in tight, submicroporous pore geometries which act as good to excellent seals. Capillary entry pressures of the best caprock lithologies are such that gas columns of the order of 300 m could potentially be trapped. The actual column height in P15 is about 125 m as indicated by RFT data. The presence of significant gas accumulations in the Main Buntsandstein in the P12, P14, P15, P18 and adjoining Q8 and Q16 blocks suggests that the P15 top-seal quality may be representative for that area.  相似文献   

Characteristics of turnover of carbonyl sulfide in four different soils     

Susanne Lehmann  Ralf Conrad 《Journal of Atmospheric Chemistry》1996,23(2):193-207

Release and uptake of carbonyl sulfide (OCS) were measured at 25°C in samples of three forest soils (BL, BW, PBE) and one soil from a rape field (RA). The soil samples were flushed with a constant flow of either air (oxic conditions) or nitrogen (anoxic conditions) containing defined concentrations of OCS. A cryogenic trapping technique with liquid argon (-186 °C) was used to collect gas samples for analysis in a gas chromatograph equipped with a flame-photometric detector. The dependence of net OCS fluxes between soil and atmosphere could be described by a simple model of simultaneous OCS production and OCS uptake. By using this model, production rates (P), uptake rate constants (k) and compensation concentrations (m _c ) of OCS could be determined as function of the soil type and the incubation conditions. Under oxic conditions, OCS production (P) and uptake were observed in all soils tested. However, the compensation concentrations (<166 ng l^-1; 1 ng OCS l^-1=0.41 ppbv) that were calculated from the model were high relative to the ambient OCS concentration (ca. 0.5 ppbv). The production rates (0.16–1.9 ng h^-1 g^-1 dw) that were actually measured when flushing the soil samples with air containing zero OCS were smaller than those (17–114 ng h^-1 g^-1 dw) calculated from the model. This observation was explained by two different concepts: one assuming the existence of a threshold concentration (m _t ) below which OCS was no longer consumed in the soil; the other assuming the existence of two different OCS consumption processes, of which only the process active at elevated OCS concentrations was covered by the experiments. The latter concept allowed the estimation of OCS compensation concentrations that were partially low enough to allow the uptake of atmospheric OCS by soil. Both OCS production and uptake in PBE soil were dependent on soil temperature (optimum 20 °C) indicating a microbial process. However, both production and consumption of OCS were not consistently inhibited by sterilization of the soil, suggesting that they were not exclusively due to microbiological processes. Under anoxic conditions, OCS was also produced, but was not consumed except in one soil (RA). Production of OCS in the soils was stimulated after addition of thiocyanate, but not thiourea, thiosulfate, thioglycolate, tetrathionate, sulfate, elemental sulfur, cysteine and methionine.  相似文献   

Flux between soil and atmosphere, vertical concentration profiles in soil, and turnover of nitric oxide: 2. Experiments with naturally layered soil cores     

Jutta Rudolph  Ralf Conrad 《Journal of Atmospheric Chemistry》1996,23(3):275-300

Intact soils cores were taken with a stainless steel corer from a sandy podzol and a loamy luvisol, and used to measure the flux (J) of NO between soil and atmosphere and the vertical profile of the NO mixing ratios (m) in the soil atmosphere, both as function of the NO mixing ratio (m _a) in the atmosphere of the headspace. These measurements were repeated after stepwise excavation of the soil column from the top, e.g. by removing the upper 2 cm soil layer. The gaseous diffusion coefficients of NO in the soil cores were either computed from soil porosity or were determined from experiments using SF6. The NO fluxes (J) that were actually measured at the soil surface were compared to the fluxes which were calculated either from the vertical NO profiles (J _c ) or from the NO production and uptake rates (J _m ) determined in the excavated soil samples. In the podzol, the actually measured (J) and the calculated (J _m , J_m) NO fluxes agreed within a factor of 2. In the luvisol, the measured NO fluxes (J) and those calculated from the vertical NO profiles (J _c ) also agreed well, but in the upper 6 cm soil layer the NO fluxes (J _m ) calculated from NO production and uptake rates were up to 7 times higher than the measured NO fluxes. This poor agreement was probably due to the inhomogeneous distribution of NO production and consumption processes and the change of diffusivities within the top layers of the luvisol. Indeed, the luvisol showed a pronounced maximum of the NO mixing ratios at about 6 cm depth, whereas the podzol column exhibited a steady and exponential decrease of the NO mixing ratios with depth. The inhomogeneities in the luvisol were confirmed by incubation of the soil cores under anoxic conditions. This treatment resulted in production of NO at several depths indicating a zonation of increased potential activities within the luvisol profile which may have biased the modelling of the NO surface flux from turnover measurements in soil samples. Inhomogeneities could be achieved even in homogenized soil by fertilization with nitrate solution.  相似文献   

灰色动态预测方法及其在变形预测中的应用     

尹晖  丁窘  张琰  邓康伟 《武汉大学学报(信息科学版)》1996,(1)

在分析比较了ＧＭ（１，１）预测模型的不足之后，提出一种实时引入新信息的等维新息和等维灰数递补组合动态预测方法。首先同常规预测法作了比较，然后进行了三峡链子崖危岩体变形发展趋势预测及有效性验证。  相似文献