Distribution of lunar impacts by objects in parabolic low inclination orbits     

Nils Aall Barricelli  Ragnar Thorbjørnsen 《Earth, Moon, and Planets》1978,18(4):479-490

This paper presents a computer investigation extending to the case of parabolic orbits, an earlier investigation conducted by Barricelli and Metcalfe (1969) on lunar impacts by external low eccentricity satellites as a means to interpret the asymmetric distribution of lunar maria. Parabolic orbits can be approximated by two kinds of objects:

1. High eccentricity external satellites may, near periapsis, approach the Moon with orbital velocity and other characteristics closely resembling those of a parabolic orbit.
2. Asteroids and meteoroids approaching the Earth-Moon system with a low velocity may have moved in a nearly parabolic orbit when they reached the lunar distance from the Earth at the time when the impacts which carved the lunar maria took place.

The investigation gives, therefore, not only additional information relevant to the interpretation of the distribution of lunar maria by the satellite impacts hypothesis (in this case high eccentricity ones), but also information about the alternative hypothesis (Wood, 1973) that asteroid impacts rather than satellite impacts were involved.  相似文献   

Alkaline fluid circulation in ultramafic rocks and formation of nucleotide constituents: a hypothesis     

Nils G Holm  Marion Dumont  Magnus Ivarsson  Cécile Konn 《Geochemical transactions》2006,7(1):7-7

Seawater is constantly circulating through oceanic basement as a low-temperature hydrothermal fluid (<150°C). In cases when ultramafic rocks are exposed to the fluids, for instance during the initial phase of subduction, ferromagnesian minerals are altered in contact with the water, leading to high pH and formation of secondary magnesium hydroxide, among other – brucite, that may scavenge borate and phosphate from seawater. The high pH may promote abiotic formation of pentoses, particularly ribose. Pentoses are stabilized by borate, since cyclic pentoses form a less reactive complex with borate. Analyses have shown that borate occupies the 2' and 3' positions of ribose, thus leaving the 5' position available for reactions like phosphorylation. The purine coding elements (adenine, in particular) of RNA may be formed in the same general hydrothermal environments of the seafloor.  相似文献   

A model of the geomagnetic field and its secular variation for epoch 2000 estimated from Ørsted data     

Nils Olsen 《Geophysical Journal International》2002,149(2):454-462

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The impact of salt on the late Messinian to recent tectonostratigraphic evolution of the Cyprus subduction zone          下载免费PDF全文

Sönke Reiche  Christian Hübscher  Axel Ehrhardt 《Basin Research》2016,28(5):569-597

Messinian evaporites of locally more than 3‐km thickness occupy the subduction zone between Cyprus and Eratosthenes Seamount. Based on a dense grid of seismic reflection profiles, we report on compressional salt tectonics and its impact on the Late Miocene to Quaternary structural evolution of the Cyprus subduction zone. Results show that evaporites have experienced significant post‐Messinian shortening along the plate boundary. Shortening has initiated allochthonous salt advance between Cyprus and Eratosthenes Seamount, representing an excellent example of salt which efficiently escapes subduction and accretion. Further east, between Eratosthenes Seamount and the Hecataeus Rise, evaporites were compressionally inflated without having advanced across post‐Messinian strata. Such differences in the magnitude of salt tectonic shortening may reflect a predominately north–south oriented post‐Messinian convergence direction, raising the possibility of a later coupling between the motion of Cyprus and Anatolia than previously thought. Along the area bordered by Cyprus and Eratosthenes Seamount a prominent step in the seafloor represents the northern boundary of a controversially debated semi‐circular depression. Coinciding with the southern edge of the salt sheet, this bathymetric feature is suggested to have formed as a consequence of compressional salt inflation and seamount‐directed salt advance. Topographic lows on top of highly deformed evaporites are locally filled by up to 700 m of late Messinian sediments. The uppermost 200 m of these sediments were drilled in the course of ODP Leg 160 and interpreted to represent Lago Mare‐type deposits (Robertson, Tectonophysics, 1998d, 298 , 63‐82). Lago Mare deposits are spatially restricted to the western part of the subduction zone, pinching out towards the east whereas presumably continuing into the Herodotus Basin further west. We suggest a sea level control on late Messinian Lago Mare sedimentation, facilitating sediment delivery into basinal areas whereas inhibiting Lago Mare deposition into the desiccated Levant Basin. Locally, early salt deformation is believed to have provided additional accommodation space for Lago Mare sedimentation, resulting in the presently observed minibasin‐like geometry.  相似文献   

Age and origin of groundwater resources in the Ararat Valley,Armenia: a baseline study applying hydrogeochemistry and environmental tracers     

Schubert  Michael  Michelsen  Nils  Schmidt  Axel  Eichenauer  Laura  Knoeller  Kay  Arakelyan  Alexander  Harutyunyan  Lilith  Schüth  Christoph 《Hydrogeology Journal》2021,29(7):2517-2527

Within the Ararat Valley (Armenia), a continuously growing water demand (for irrigation and fish farming) and a simultaneous decline in groundwater recharge (due to climate change) result in increasing stress on the local groundwater resources. This detrimental development is reflected by groundwater-level drops and an associated reduction of the area with artesian conditions in the valley centre. This situation calls for increasing efforts aimed at more sustainable water resources management. The aim of this baseline study was the collection of data that allows for study on the origin and age distribution of the Ararat Valley groundwater based on environmental tracers, namely stable (δ²H, δ¹⁸O) and radioactive (³⁵S, ³H) isotopes, as well as physical-chemical indicators. The results show that the Ararat Valley receives modern recharge, despite its (semi-)arid climate. While subannual groundwater residence times could be disproved (³⁵S), the detected ³H pattern suggests groundwater ages of several decades, with the oldest waters being recharged around 60 years ago. The differing groundwater ages are reflected by varying scatter of stable isotope and hydrochemical signatures. The presence of young groundwater (i.e., younger that the 1970s), some containing nitrate, indicates groundwater vulnerability and underscores the importance of increased efforts to achieve sustainable management of this natural resource. Since stable isotope signatures indicate the recharge areas to be located in the mountains surrounding the valley, these efforts must not be limited to the central part of the valley where most of the abstraction wells are located.

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Automated tracking of fish in trawls using the DIDSON (Dual frequency IDentification SONar)   总被引：1，自引：0，他引：1  

Handegard  Nils Olav; Williams  Kresimir 《ICES Journal of Marine Science》2008,65(4):636-644

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Flow dynamics,sedimentation and erosion of glacial lake outburst floods along the Middle Pleistocene Scandinavian Ice Sheet (northern central Europe)          下载免费PDF全文

Jutta Winsemann  Petteri Alho  Leena Laamanen  Nils Goseberg  Jörg Lang  Josef Klostermann 《Boreas: An International Journal of Quaternary Research》2016,45(2):260-283

During the Middle Pleistocene late Saalian glaciation of northern central Europe numerous pro‐glacial lakes formed along the southwestern margin of the Scandinavian Ice Sheet. Little is known about the drainage history of these lakes, the pathways of glacial lake outburst floods and their impacts on erosion, sedimentation and landscape evolution. This study investigated the impact of the late Saalian Weser and Münsterland Lake (Germany) outburst floods. In particular, we reconstructed the routing and flow dynamics of the lake outburst flood and analysed the flood related sediments. We employed one‐dimensional hydraulic modelling to calculate glacial lake outburst flood hydrographs. We modelled the flow pathway and local flow conditions along the pathway based on the boundary conditions of two different hydrographs and two different ice‐margin positions. The modelling results were compared with geomorphological and sedimentological field data in order to estimate the magnitude and impact of the flood on erosion and sedimentation. Two major lake drainage events are reconstructed for the study area, during which approximately 90–50 km³ of water was released. Modelling results indicate that the lake outburst floods created a high‐energy flood wave with a height of 35–50 m in confined valley areas that rapidly spread out into the Lower Rhine Embayment eventually flowing into the North Sea basin. The sedimentary record of the outburst floods comprises poorly sorted coarse‐grained gravel bars, long‐wavelength bedforms and sandy bedforms deposited by supercritical and subcritical flows. Some parts of the sandy flood deposits are rich in reworked mammoth bones or mammoth and horse teeth, pointing to reworking of older fluvial sediments, hydraulic concentration and subsequent re‐sedimentation of vertebrate remains. These deposits are preserved in sheltered areas or at high elevations, well above the influence of postglacial fluvial erosion. The flood‐related erosional features include up to 80‐m‐deep scour pools, alluvial channels and streamlined hills.  相似文献   

Morphology,perfection and growth of natural pyrite whiskers and thin platelets     

I. K. Bonev  M. Reiche  M. Marinov 《Physics and Chemistry of Minerals》1985,12(4):223-232

Whiskers and thin platelets of pyrite have been found growing coherently on the face of small cubic pyrite crystals from the Strashimir and Gradishte hydrothermal lead-zinc deposits. The host crystals formed framboids and spheroids of macroscopic size inside large crystals of chalcopyrite from which they are separated by concentric gaps. The whiskers, one to several μm in width, are elongated along [001] and bounded by {100}, partly by {210} and {111} faces. Scanning electron microscopic (SEM) observation revealed longitudinal steps and grooves, flat rectangular pits, drop-like and elongated bulges on their side faces. High-voltage electron microscopic (HVEM) studies showed that the thin whiskers are perfect and dislocation-free, although some ribbon-like whiskers and platelets contain internal longitudinal channels and small isometric fluid inclusions. Based on these observations, the following growth mechanism is proposed. Whiskers grow in the restricted volume of the internal cavities in chalcopyrite from stagnant solutions under a diffusion regime. The growth proceeds in two stages: (1) Initially, pyramidal “pedestals” are formed due to morphological instability of the host crystal surfaces and multiapex growth, (2) Whiskers grow rapidly by unidirectional supply of material and competition between neighbouring individual whiskers, the growth taking place at the tip by a two-dimensional nucleation mechanism. The whiskers and thin platelets are considered to be peculiar highly anisometric skeletal crystals.  相似文献   

β-FeOOH · Cl_n (akaganéite) and Fe_1-xO (wüstite) in hot brine from the Atlantis II Deep (Red Sea) and the uptake of amino acids by synthetic β-FeOOH · Cl_n     

Nils G Holm  Michael J Dowler  Tommy Wadsten  Gustaf Arrhenius 《Geochimica et cosmochimica acta》1983,47(8):1465-1470

A yellowish brown precipitate in samples of Red Sea hot brine has been identified as β-FeOOH · Cl_n (akaganéite) by Guinier-Hägg X-ray diffraction techniques, transmission electron microscopy (TEM), electron diffraction and electron excited X-ray fluorescence. Microcrystals of Fe_1-xO (wüstite) were also identified by electron diffraction. Synthetic β-FeOOH · Cl_n characterized by the same techniques was identical with the brine precipitate.Bonding between β-FeOOH · Cl_n and ¹⁴C labeled amino acids is pH dependent: between pH 3 and pH 7.6 amino acids were bound to the extent of 40 to 60% or 0.6 to 0.9 mmol per kg of iron oxide hydroxide. Some selectivity in affinity for different amino acids was observed, however, the effect is insufficient to explain the unusual distribution in the Atlantis II Deep brine reported in the literature.  相似文献   

A three-dimensional geophysical model of the crust in the Barents Sea region: model construction and basement characterization   总被引：2，自引：0，他引：2  

Oliver Ritzmann  Nils Maercklin  Jan Inge Faleide  Hilmar Bungum  Walter D. Mooney  Shane T. Detweiler 《Geophysical Journal International》2007,170(1):417-435

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