Megaregolith evolution and cratering cataclysm models—Lunar cataclysm as a misconception (28 years later)     

William K. Hartmann 《Meteoritics & planetary science》2003,38(4):579-593

Abstract— The hypothesis of a lunar cataclysmic cratering episode between 3.8 and 3.9 Gyr ago lacks proof. Its strongest form proposes no cratering before about 4.0 Gyr, followed by catastrophic formation of most lunar craters and basins in >200 Myr. The premise that “zero impact melts implies zero impacts” is disproved by data from asteroids, on which early collisions clearly occurred, but from which early impact melts are scarce. Plausible cataclysm models imply that any cataclysm should have affected the whole inner solar system, but among available lunar and asteroid impact melt and impact age resetting data, a narrow, strong 3.8–3.9 Gyr spike in ages is seen only in the region sampled by Apollo/Luna. Reported lunar meteorite data do not show the spike. Asteroid data show a broader, milder peak, spreading from about 4.2 to 3.5 Gyr. These data suggest either that the spike in Apollo impact melt ages is associated with unique lunar front side events, or that the lunar meteorites data represent different kinds of events than the Apollo/Luna data. Here, we develop an alternate “megaregolith evolution” hypothesis to explain these data. In this hypothesis, early impact melts are absent not because there were no impacts, but because the high rate of early impacts led to their pulverization. The model estimates survival halflives of most lunar impact melts prior to 4.1 Gyr at >100 Myr. After a certain time, T_critical ?4.0 Gyr, impact melts began to survive to the present. The age distribution differences among impact melts and plutonic rocks are controlled by, and hold clues to, the history of regolith evolution and the relative depths of sequestration of impact melts versus plutonic rocks, both among lunar and asteroidal samples. Both the “zero cratering, then cataclysm” hypothesis and the “megaregolith evolution” hypothesis require further testing, especially with lunar meteorite impact melt studies.  相似文献   

Electromagnetic and geoelectric investigation of the Gurinai Structure, Inner Mongolia, NW China   总被引：2，自引：0，他引：2  

S. Hlz  D. Polag  M. Becken  R. Fiedler-Volmer  H.C. Zhang  K. Hartmann  H. Burkhardt 《Tectonophysics》2007,445(1-2):26

In three field campaigns between the years 2000 and 2004 geophysical measurements were conducted in the Ejina Basin, NW China. Research work in the year 2004, which is described in this paper, was concentrated on the Gurinai Structure (101°25′E, 41°N) situated in the southeastern part of the Ejina Basin in transition to the dune fields of the Badain Jaran Shamo. On satellite images the Gurinai Structure can be identified by two almost 100 km long, subparallel, N–S-striking lineaments, which may indicate tectonic deformations of late Quaternary sediments. To get a coherent picture of the structure a geophysical survey employing three electromagnetic methods – magnetotellurics (MT), transient electromagnetics (TEM), and geoelectrics (DC) – has been conducted to map the subsurface resistivity at different depth scales.The geophysical data interpretation for shallow and intermediate depth down to a few hundred meters links the subsurface distribution of electric resistivity to geomorphological units known from field work in reference with satellite images. The westerly lineament of the Gurinai Structure coincides with a subvertical change in electric resistivity. Together with geomorphological indications from fieldwork and the analysis of elevation data (SRTM), a tectonic deformation of unconsolidated sediments along a fault with an extensional component is interpreted. In the central and eastern part of the Gurinai Structure a shallow resistive subsurface layer can be traced into the first dunes of the Badain Jaran Shamo. This resistive subsurface layer is linked to the presence of fresh water, indicating infiltration from the dune field. Also, in the eastern part of the Gurinai Structure a resistive, approximately ENE-striking feature can be seen at intermediate depth, which is interpreted as a crystalline basement ridge. Towards the southern margin of the Gurinai Structure a trough-shaped unit with low resistivities and a thickness of about 1 km is identified and can be explained by a sediment package saturated with fluids of high salinity or substantial amounts of clay. The strike direction of the structure can be connected to the regional pattern of tectonic faults and seismicity.The interpretation of electromagnetic data at various depth scales contributes to the general understanding of the Ejina Basin's buildup and tectonic setting in the vicinity of the Gurinai Structure.  相似文献   

Chemical Aspects of Fractional Crystallization of Fatty Acid Methyl Esters Produced from Waste Fats     

Taher Sahlabji  Hubertus Wichmann  Heike Dieckmann  Petra Jopke  Müfit Bahadir 《洁净——土壤、空气、水》2007,35(4):323-328

Fractional crystallization of fatty acid methyl esters (FAME) produced from waste cooking oil or animal fats was performed in a laboratory-scale facility. The raw esters and the “winterization” products were analyzed by determining the FAME pattern, iodine and peroxide numbers as well as oxidation stabilities and element concentrations. Fractionation experiments under air and nitrogen were conducted, but no differences concerning oxidative stability were observed. By improvement of the winterization and washing the filtration residue with methanol, the enrichment of saturated FAME in one step was raised up to a technically sufficient rate of 85%. Absorption of oxygen by FAME at different temperatures was measurable. Volatile decomposition products were registrated after heating the FAME at different temperatures. It was shown that antioxidants like butylhydroxytoluene or α-tocopherol were enriched in the phase of unsaturated FAME. This effect obviously affected the oxidative stability of the fraction of saturated FAME during winterization, although no oxidative damage of FAME was detectable at temperatures up to 20°C.  相似文献   

Dissolved inorganic nutrients and organic substrates in the River Warnow (North-Eastern Germany) – Utilisation by bacterioplankton     

Heike M. Freese  Solvig Grs  Ulf Karsten  Rhena Schumann 《Limnologica》2007,37(3):264-277

After 1990, external loads of Central European rivers with inorganic nutrients (nitrogen and phosphorus) and organic material were reduced because of changed environmental laws. However, in the eutrophic lowland River Warnow, North-Eastern Germany, nitrate concentrations remained high with 35–185 μmol l⁻¹ without a significant decrease since 1992. In contrast, phosphate concentrations, varying between 0.3 and 5.2 μmol l⁻¹ during the growth season 2002, decreased significantly over the years. However, its concentrations still exceeded 1 μmol l⁻¹ regularly in the growth seasons. This load led to a substantial accumulation of organic matter additional to high terrestrial inputs. Despite the high organic load, the remineralising bacteria were mainly inactive in River Warnow. Therefore, the composition of the dissolved organic material, especially its bioavailability, were investigated during the growth season 2002 and discussed with other potential controlling factors. River Warnow carried a high load of dissolved organic carbon (14 mg l⁻¹), especially of humic substances (5.5 mg C l⁻¹). Bacterial abundance (12×10⁶ ml⁻¹) as well as production (1.7 μg C l⁻¹ h⁻¹) depended on temperature. During late spring and summer at constantly higher temperatures, bacterial production correlated positively to readily utilisable substrates and to humic compounds. Thus, the bacterial community in River Warnow may be well adapted or contain enough species using the available amino acids and carbohydrates as well as humic matter compounds. However, calculated from protozoan biomass, grazing may control bacterial biomass and perhaps community composition profoundly, what lead to the low percentages of active bacteria.  相似文献   

Geographic distribution of Tetracapsuloides bryosalmonae infected fish in Swiss rivers: an update     

Thomas Wahli  Daniel Bernet  Pascale April Steiner  Heike Schmidt-Posthaus 《Aquatic Sciences - Research Across Boundaries》2007,69(1):3-10

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Assessment of fish health status in four Swiss rivers showing a decline of brown trout catches   总被引：2，自引：0，他引：2  

Simone Zimmerli  Daniel Bernet  Patricia Burkhardt-Holm  Heike Schmidt-Posthaus  Pascal Vonlanthen  Thomas Wahli  Helmut Segner 《Aquatic Sciences - Research Across Boundaries》2007,69(1):11-25

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Preliminary mariner 9 report on the geology of Mars     

J.F. McCauley  M.H. Carr  J.A. Cutts  W.K. Hartmann  Harold Masursky  D.J. Milton  R.P. Sharp  D.E. Wilhelms 《Icarus》1972

Mariner 9 pictures indicate that the surface of Mars has been shaped by impact, volcanic, tectonic, erosional and depositional activity. The moonlike cratered terrain, identified as the dominant surface unit from the Mariner 6 and 7 flyby data, has proven to be less typical of Mars than previously believed, although extensive in the mid- and high-latitude regions of the southern hemisphere. Martian craters are highly modified but their size-frequency distribution and morphology suggest that most were formed by impact. Circular basins encompassed by rugged terrain and filled with smooth plains material are recognized. These structures, like the craters, are more modified than corresponding features on the Moon and they exercise a less dominant influence on the regional geology. Smooth plains with few visible craters fill the large basins and the floors of larger craters; they also occupy large parts of the northern hemisphere where the plains lap against higher landforms. The middle northern latitudes of Mars from 90 to 150† longitude contain at least four large shield volcanoes each of which is about twice as massive as the largest on Earth. Steep-sided domes with summit craters and large, fresh-appearing volcanic craters with smooth rims are also present in this region. Multiple flow structures, ridges with lobate flanks, chain craters, and sinuous rilles occur in all regions, suggesting widespread volcanism. Evidence for tectonic activity postdating formation of the cratered terrain and some of the plains units is abundant in the equatorial area from 0 to 120° longitude.Some regions exhibit a complex semiradial array of graben that suggest doming and stretching of the surface. Others contain intensity faulted terrain with broader, deeper graben separated by a complex mosaic of flat-topped blocks. An east-west-trending canyon system about 100–200 km wide and about 2500 km long extends through the Coprates-Eos region. The canyons have gullied walls indicative of extensive headward erosion since their initial formation. Regionally depressed areas called chaotic terrain consist of intricately broken and jumbled blocks and appear to result from breaking up and slumping of older geologic units. Compressional features have not been identified in any of the pictures analyzed to data. Plumose light and dark surface markings can be explained by eolian transport. Mariner 9 has thus revealed that Mars is a complex planet with its own distinctive geologic history and that it is less primitive than the Moon.  相似文献   

Moon: ‘ghost’ craters formed during mare filling     

D. P. Cruikshank  W. K. Hartmann  C. A. Wood 《Earth, Moon, and Planets》1973,7(3-4):440-452

This paper discusses formation of pathological cases of crater morphology due to interaction of craters with molten lavas. Terrestrial observations of such a process are discussed. In lunar maria, a number of small impact craters (D < 10 km) may have been covered by thin layers of fluid lavas, or formed in molten lava. Some specific lunar examples are discussed, including unusual shallow rings resembling experimental craters deformed by isostatic filling.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.  相似文献   

Midsummer Energy Balance for the Southern Seas     

Gerd Wendler  Brian Hartmann  Chris Wyatt  Martha Shulski  Henry Stone 《Boundary-Layer Meteorology》2005,117(1):131-148

During a ship voyage from Tasmania to Antarctica in summer 2000/01, radiative and meteorological measurements were continuously made, from which the surface energy budget was calculated. Sea conditions throughout the voyage ranged from open water to broken pack and finally to snow-covered unbroken sea ice in McMurdo Sound. The global radiation increased on average during the trip (to higher latitudes) as we travelled poleward. The net radiation, which was positive (toward the surface) on average, decreased however, mostly due to the increase in surface albedo. For open water, most of the net radiation is used for evapouration (61%), while for broken sea-ice conditions, nearly all energy is used for melting of the sea ice or heating of the ocean (96%). For unbroken snow-covered sea ice, the net radiation lies close to zero, due to the high surface albedo, which reached a mean value of 0.81. The sensible heat flux becomes the largest heat source and nearly all the energy is used for warming of the surface. Finally, a Radarsat image, on which the ship track was visible, was used to compare the ship observations with satellite derived ice types.  相似文献   

Trends in Extreme Precipitation Events in the Indus River Basin and Flooding in Pakistan     

Heike Hartmann  Hilary Buchanan 《大气与海洋》2014,52(1):77-91

In the absence of a sufficiently dense network of climate stations covering all topographic regions of the Indus River basin and delivering high quality data over the last 30 years or more, daily precipitation data were obtained from the National Centers for Environmental Prediction-Department of the Enviornment (NCEP-DOE) Reanalysis 2 dataset for the period 1979 to 2011. The daily precipitation data were transformed into time series of frequency of extreme precipitation events of 1-day and 10-day durations defined in terms of 90th and 99th percentile threshold exceedances. The non-parametric Mann-Kendall trend test was applied to determine whether statistically significant changes in precipitation extremes occurred over time, in due consideration of autocorrelation in the data.

Extreme precipitation showed a high spatial variability, with the highest daily and 10-day precipitation totals, and thus highest 90th and 99th percentiles, in the southeastern lowlands at the foot of the Himalayas and the lowest in the Karakorum. Significantly decreasing trends in extreme precipitation were observed in the western part of the Indus River basin; significantly increasing trends were mainly detected in the very high mountainous regions in the east (Transhimalaya and Himalayas) and in the north (Hindu Kush and Karakorum) of the Indus basin. High precipitation rates are not common in the arid climate of these high mountainous regions. Future flood management plans need to consider the increasing trends in extreme precipitation events in these areas.  相似文献