The Earth. Its origin, structure and evolution: M.W. McElhinny (Editor). Academic Press, London-New York- San Francisco, 1979, 597 pp., $ 7     

Hans Christian Larsen  David Bridgwater 《Tectonophysics》1980,68(3-4)

  相似文献   

Carbon isotope geochemistry of the 3.7 × 10⁹-yr-old Isua sediments,West Greenland: implications for the Archaean carbon and oxygen cycles     

Manfred Schidlowski  Peter W.U Appel  Rudolf Eichmann  Christian E Junge 《Geochimica et cosmochimica acta》1979,43(2):189-199

One hundred and twenty-four carbonate samples from the meta-sedimentary sequence of the 3.7 × 10⁹ yr old Isua supracrustal belt (W-Greenland) have yielded a δ¹³C_carb average of ?2.5 ± 1.7%. vs PDB and a δ¹⁸O_carb average of +13.0 ± 2.5%. vs SMOW. The oxygen mean comes fairly close to the averages of other early Precambrian carbonates. The carbon average, however, is some 2%. more negative than those of younger marine carbonates. In terms of a simple terrestrial ¹³C mass balance, if δ¹³C_carb values are original sedimentary values, this more negative δ¹³C average would imply a considerably smaller $\text{C}{}_{\mathrm{org}}\text{C}{}_{\mathrm{carb}}$ ratio in the sedimentary shell during Isua times, and would thus support the concept of a gradual buildup of a sedimentary reservoir of organic carbon during the early history of the Earth. Since, however, the Isua supracrustal rocks have experienced amphibolite-grade metamorphism, which in other areas has been shown to lower δ¹³C_carb values, it is most likely that the original values of these rocks were approx 0%.. This indicates that C_orx and C_carb were present in the ancient carbon reservoir in about ‘modern’ proportions. Unless this early stabilization of the terrestrial carbon cycle in terms of a constant partitioning of carbon between the reduced and oxidized species is shown to have been caused by some inorganic geochemical process, a considerably earlier start of chemical evolution and spontaneous generation of life must be considered than is presently accepted.  相似文献   

Coastal and near-shore changes correlated with die-back in eel-grass (Zostera Marina,L.)     

Christian Christiansen  Henning Christoffersen  JØrgen Dalsgaard  Per NØrnberg 《Sedimentary Geology》1981,28(3):163-173

The die-back of eel-grass (Zostera marina, L.) is found to have played an important role with regard to near-shore sedimentation and coastal changes.In a natural harbour at Kyholm, Denmark a hiatus is found between silty sediments that date from about 4000 BC and overlying modern sandy sediments. It is suggested that this is a consequence of the die-back of eel-grass in the nineteen-thirties, resulting in mobilisation and disturbance of nearshore sediments and the shoreward movement of mobilised sandy material into the harbour. The coastal morphology of Kyholm was relatively stable from 1802 to 1933, but between 1933 and 1978 there have been two periods of drastic progradation correlated with die-back of eel-grass.  相似文献   

Combining a rainfall–runoff model and a regionalization approach for flood and water resource assessment in the western Po Valley,Italy     

Alessio Cislaghi  Daniele Masseroni  Christian Massari  Stefania Camici  Luca Brocca 《水文科学杂志》2020,65(3):348-370

ABSTRACT

Selecting the best structure and parameterization of rainfall–runoff models is not straightforward and depends on a broad number of factors. In this study, the “Modello Idrologico Semi-Distribuito in continuo” (MISDc) was tested on 63 mountainous catchments in the western Po Valley (Italy) and the optimal model parameters were regionalized using different strategies. The model performance was evaluated through several indexes analysing hydrological regime, high-flow condition and flow–duration curve (FDC). In general, MISDc provides a good fit behaviour with a Kling-Gupta Efficiency index greater than 0.5 for 100% and 84% of cases for calibration and validation, respectively. Concerning the regionalization, spatial proximity approach is the most accurate solution obtaining satisfactory performance. Lastly, the predicted FDCs showed an excellent similarity with the observed ones. Results encourage to apply MISDc over the study area for flood forecasting and for assessing water resources availability thanks to the modest computational efforts and data requirements.  相似文献   

Precambrian sedimentary carbonates: carbon and oxygen isotope geochemistry and implications for the terrestrial oxygen budget   总被引：2，自引：0，他引：2  

Manfred Schidlowski  Rudolf Eichmann  Christian E. Junge 《Precambrian Research》1975,2(1):1-69

Carbon isotope values of 260 Precambrian limestones and dolomites (most of them being substantially unaltered) have yielded an overall mean of $\text{δ}{}^{13}\text{C}\text{= +0.4 ± 2.7‰}$ vs. PDB; the corresponding oxygen values average at $\text{δ}{}^{13}\text{O = +20.0 ± 4.2‰}$ vs. SMOW. Like the overall mean, the δ ¹³C values furnished by individual carbonate occurrences are, as a rule, fairly “modern” and almost constant as from the very beginning of the sedimentary record. A remarkable exception are the “heavy” dolomites of the Middle Precambrian Lomagundi Group, Rhodesia, with $\text{δ}{}^{13}\text{C}\text{= +9.4 ± 2.0‰}$ vs. PDB. As a result of our measurements, the sporadic occurrence in the geological past of anomalously heavy carbonates seems to be established.The approximate constancy around zero per mill of the δ ¹³C values of marine carbonates through geologic time would imply a corresponding constancy of the relative proportion of organic carbon in the total sedimentary carbon reservoir since about 3.3 · 10⁹ y ago (with C_org/C_total ? 0.2). Utilizing this ratio and current models for the accumulation of the sedimentary mass as a function of time, we get a reasonable approximation for the absolute quantity of organic carbon buried in sediments and, accordingly, of photosynthetic oxygen released. Within the constraints of our model (based on a terrestrial degassing constant λ = 1.16 · 10^?9 y^?1) close to 80% of the amount of oxygen contained in the present oxygen budget should have been released prior to 3 · 10⁹ y ago. Since geological evidence indicates an O₂-deficient environment during the Early and most parts of the Middle Precambrian, there is reason to believe that the distribution of this oxygen between the “bound” and the “molecular” reservoir was different from that of today (with effective O₂-consuming reactions bringing about an instantaneous transfer to the crust of any molecular oxygen released). Accordingly, the amount of C_org in the ancient sedimentary reservoir as derived from our isotope data is just a measure of the gross amount of photosynthetic oxygen produced, withholding any information as to how this oxygen was partitioned between the principal geochemical reservoirs. As a whole, the carbon isotope data accrued provide evidence of an extremely early origin of life on Earth since the impact of organic carbon on the geochemical carbon cycle can be traced back to almost 3.5 · 10⁹y.  相似文献   

Fractionnement des éléments en trace Li,Rb, Ba,Sr dans les séries andésitiques et shoshonitiques du Pérou. Comparaison avec d'autres zones orogéniques     

Claude Dupuy  Dr. Christian Lefèvre 《Contributions to Mineralogy and Petrology》1974,46(2):147-157

In the calc-alkaline rocks of Peru, the rubidium content and the K/Ba, Rb/Sr ratios increase, while the strontium content and the K/Rb, Ba/Rb ratios decrease according to the distance of the trench. It is suggested that theses variations are related to a fractionation of plagioclase and contamination with differential migration of mobile elements. A comparative study between andesites of various localities shows in Peru an enrichment in Rb, Sr and Ba and a disparition of the Rb-Ba correlation; this last observation looks characteristic of continental margin andesites. The shoshonitic rocks differ from the andesites by a high content of Sr and Ba. The genetic relationships between these two kinds of rocks are discussed. It appears that the shoshonites are originated from a different magmatic source.  相似文献   

Buchbesprechungen     

Christian Zimmermann  K. Wuhrmann  HR. Bürgi  Peter Perret  K. Klingler 《Aquatic Sciences - Research Across Boundaries》1973,35(1):196-200

Ohne Zusammenfassung  相似文献   

Zonal mean circulation at the cloud level on Venus: Spring and fall 1979 OCPP observations     

Sanjay S. Limaye  Christian J. Grund  Steven P. Burre 《Icarus》1982,51(2):416-439

Cloud motions were obtained from a number of images acquired in reflected solar ultraviolet light during spring and fall of 1979 from the Pioneer Venus Orbiter Cloud Photopolarimeter (OCPP) to determine the zonal mean circulation of the atmosphere of Venus at the cloud top level. The meridional profile of the zonal component of motion is somewhat different from that previously obtained from Mariner 10 and preliminary Pioneer Venus observations, although the equatorial magnitude is about the same (?94 m/sec). The mean meridional motion is toward the south pole south of about 5° south latitude, and toward the north pole north of this latitude, with peak mean magnitudes of about 7 m/sec polewards of 20° north and 40° south latitudes in the respective hemispheres. From the few measurements obtained at higher latitudes the magnitude of the mean meridional component appears to decrease although it is still directed toward the respective poles. Due to the evolution of the cloud patterns over the duration of the images from which the cloud velocities are obtained, the uncertainties in the mean zonal and meridional components may be as large as 5–10 and 2–4 m/sec, respectively. Preliminary estimates of meridional momentum transport show that the mean circulation dominates the eddy circulation transport completely, in agreement with the estimates obtained from Mariner 10 data, although the uncertainties in both the mean and eddy circulation transports are large. The momentum transports are polewards and their peak magnitudes occur at latitudes between 20° and 40° in both the hemispheres.  相似文献   

Bahamian carbonate platform development in response to sea-level changes and the closure of the Isthmus of Panama   总被引：1，自引：0，他引：1  

John?J.?ReijmerEmail author  Christian?Betzler  Dick?Kroon  Ralf?Tiedemann  Gregor?P.?Eberli 《International Journal of Earth Sciences》2002,91(3):482-489

In this paper we show that the development of the sediment architecture at the leeward toe-of-slope of Great Bahama Bank (Ocean Drilling Project Leg 166, Bahama Transect) during the last 6 Ma is not only a response to sea-level fluctuations, but also to major paleo-oceanographic and climatic changes. A major sequence boundary close to the Miocene/Pliocene boundary (dated at 5.6-5.4 Ma) is interpreted to reflect a major sea-level drop that was followed by a sea-level rise, which led to the re-flooding of the Mediterranean Sea at the end of the Messinian and increasing sea-surface temperatures at Great Bahama Bank. Distinct erosional horizons occurred during the Pliocene (dated at 4.6 and 3.3-3.6 Ma) related to sea-level change and the intensification of the Gulf Stream when the emergence of the Isthmus of Panama reached a critical threshold. The Gulf Stream brings warm, saline and nutrient-poor waters to the Bahamas. Starting at the Early-Late Pliocene boundary at 3.6 Ma this paleo-oceanographic reorganization in combination with enhanced sea-level fluctuations associated with the Late Pliocene main intensification in Northern Hemisphere Glaciation (since 3.2 Ma) led to (1) a gradual change from a ramp-type to a flat-topped type morphology, and (2) a change from a skeletal to a non-skeletal-dominated sedimentary system (mainly peloidal). Increased sea-level fluctuations during the second half of the Pleistocene led to an intensified high stand-shedding depositional pattern within the surrounding basins.  相似文献   

Lake Jezero v Ledvici (NW Solvenia) – changes in sediment records over the last two centuries     

Anton Brancelj  Milijan Šiško  Gregor Muri  Peter Appleby  Andrea Lami  Ewan Shilland  Neil L. Rose  Christian Kamenik  Stephen J. Brooks  John A. Dearing 《Journal of Paleolimnology》2002,28(1):47-58

Lake Jezero v Ledvici (NW Slovenia) is a 14 m deep mountain lake at an elevation of 1860 m, situated on limestone bedrock. It is an oligotrophic, alkaline and hard-water lake with a transparency of about 14 m and has suffered several times over recent centuries from strong earthquakes. In 1996 five sediment cores, between 35 and 45 cm long, were collected from the deepest part of the lake and analysed to reconstruct environmental changes over the last few centuries. The data indicate changes induced by pollution and climate change during the last two centuries similar to those in other European mountain and remote lakes. However, at this site earthquakes have also affected the lake and partly obscure the interpretation of the sediment record. From 1780 to 1890, sediment records show low abundance of diatoms and relatively high abundance of Cladocera. After 1890, the number of diatoms started to increase coinciding with a strong earthquake. From the beginning of the 20th century, concentrations of spheroidal carbonaceous particles (SCP), diatom valves and head capsules of chironomids gradually increased whilst in Cladocera the main difference observed was a change in the proportion of benthic taxa. After 1960, in parallel with a rise in air temperature, a further increase in accumulation rate of diatoms started, but there was a decrease in Cladocera.  相似文献