美国艾奥瓦州文尼希克Lagerst(a)tte及其沉积环境

Lagerstatte是指保存丰富或精美化石、因而具有特殊研究价值的化石层.这类地层所含的化石常具有经矿化的生物软体甚至未变实体,从而为古生物的分类学、组织学、形态学、解剖学、生态学、埋藏学等研究提供了极其难得的材料.近年来发现于美国艾奥瓦州的文尼希克化石层,以其特异保存的多门类不常见化石分子为特征,成为目前仅知的中奥陶世Lagerstatte.这一生物群的发现不仅填补了化石记录中的一些空白,也为中奥陶世的生物辐射事件研究领域打开了一个在赤道附近非正常海洋环境中生存的生物群面貌窗口.而且,其中所含的不同类别矿化生物残留,在有机物的分解、置换以及生物成岩作用等研究中具有重要意义.初步研究表明,文尼希克生物群的生活环境与化石保存,可能与陨石撞击事件有关,从而为奥陶纪生物辐射事件的起因町能与太空星体爆裂有关的理论研究,提供了新的验证材料.     

On the interpretation of the “inverse phase effect” for CO2 equivalent widths on Venus

Computations of the equivalent widths of absorption lines as a function of planetary phase angle are made for a homogeneous cloud with particles having the properties (shape, refractive index, and size distribution) deduced from polarimetry of Venus. The computed equivalent widths show an “inverse phase effect” comparable to that which is observed for CO₂ lines on Venus. This result verifies a recent suggestion of Regas et al. that the existence of an inverse phase effect does not by itself imply the presence of multiple layers of scattering particles in the atmosphere of Venus.     

Formation of spectral lines in planetary atmosphere IV. Theoretical evidence for structure of the jovian clouds from spectroscopic observations of methane and hydrogen quadrupole lines

The theory of formation of pressure-broadened methane lines and collision-narrowed hydrogen quadrupole lines in a Jovian atmosphere is studied in detail for a physically realistic model of the planet's lower atmosphere. Only observations of the center-to-limb (CTL) variations of the equivalent width of absorption lines for both of these molecules can identify the structure of the visible cloud layers. Observations of the CTL variation of methane and hydrogen quadrupole lines are the most suitable for studying the Jovian atmosphere. The CTL variations for hydrogen are much greater and more sensitive to variations of the properties of the thin upper tropospheric cloud layer than the corresponding observations of methane lines. A detailed comparison of hydrogen quadrupole with methane lines is made for the same continuum conditions, enabling us to develop a detailed understanding of the formation of the collision-narrowed hydrogen quadrupole lines in a Jovian atmosphere.     

Mars: Evidence for dynamic processes from mariners 6 and 7

Mariners 6 and 7 photographs of the equatorial region of Mars document a three-stage evolution of that part of the Martian surface: (1) High- and intermediate-albedo cratered terrains in Meridiani Sinus, Margaritifer Sinus-Thymiamata, Deucalionis Regio-Sabaeus Sinus, and Hellespontus; (2) low-albedo moderately cratered terrain and dark crater fill in Meridiani Sinus, Thymiamata, and Deucalionis Regio-Sabaeus Sinus and possible volcanism in the Hellas-Hellespontus border; and (3) high-albedo surficial deposits, banked-up crater fill, a possible bright-ray crater in Meridiani Sinus, chaotic terrain on the edge of the Margaritifer Sinus mesa, featureless terrain in Hellas and Edom, sinuous channel-like reentrants on scarps at the Hellas-Hellespontus boundary. Regional faulting seems to have occurred following formation of the old cratered plains and prior to formation of low-albedo plains in Meridiani Sinus and also prior to formation of canyon-like reentrants and featureless terrain along the Hellas-Hellespontus boundary.Mars has had a complex history of dynamic evolution, possibly analogous to the more stable regions of Earth. Its geochemical differentiation and thermal regime should account for long-term postaccretional tectonic and volcano-tectonic processes as well as for fluid media on its surface sufficient to cause erosion, including the cutting of large canyons.     

The slab thickness of the mid-latitude ionosphere

The thickness of the peak of the ionosphere depends primarily on the temperature T _n of the neutral gas, and corresponds approximately to an α-Chapman layer at a temperature of 0.87T _n. The overall slab thickness, as given by Faraday rotation measurements, is then τ =0.22 _n + 7km. Expansion of the topside ionosphere, and changes in the E-andFl-regions increase τ by about 20 km during the day in summer. Near solar minimum τ is increased by a lowering of the O ⁺/H ⁺ transition height; if the neutral temperature T _n is estimated, this height can be obtained from observed values of τ.Hourly values of slab thickness were determined over a period of 6 yr at 34°S and 42°S. Near solar maximum the night-time values were about 260 km in all seasons. The corresponding neutral temperatures agree with satellite drag values; they show a semiannual variation of 14 per cent and a seasonal change of 5 per cent. Daytime values of τ were about 230 km in winter and 320 km in summer, implying a seasonal change of 30 per cent in T _n. Temperatures increase steadily throughout the day in all seasons, with a rapid post-sunset cooling in summer. Downwards movements produce a large peak in τ at 0600 hr in winter. A large upwards flux, equal to about 40 per cent of the maximum (limiting) value, reduces τ for several hours after sunrise in winter. The slab thickness increases near solar minimum showing a reduction of the O ⁺/H ⁺ transition height to about 700 km in summer and 500 km in winter.     

The use of the saros in lunar dynamical studies

It is shown that the near-periodicity in the Earth-Moon-Sun system demonstrated by the possibility of using the Saros to predict eclipses, suggests that the Saros can also be used in a fast and accurate method of special perturbations which can be applied for long term study of the evolution of the Moon's orbit.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.     

Magnetic fields around highly magnetized objects

The structure of the magnetic fields of a collapsed star is studied by tracing the flux lines in the quasi-vacuum approximation. The existence of a magnetic neutral line in a system of reference corotating with the star is studied, where magnetic energy dissipations into particle kinetic energy via plasma instabilities could occur.     

High-resolution photography of the solar chromosphere

High-resolution filtergrams of the quiet chromosphere, taken at seven wavelengths in H with the aid of a computer-controlled 1/8 Å filter, have been used to derive the contrast of ten bright and dark mottles as functions of wavelength. The contrast profiles of bright and dark mottles are strikingly different. They disagree with Athay's (1970) velocity model but, with an appropriate choice of parameters, can be brought into good agreement with Beckers' (1964) cloud model. Comparison between observation and theory yields values for the source function S, optical thickness t ₀, line broadening parameter ₀, and line-of-sight velocity V for both bright and dark mottles. The values of S and t ₀ obtained for dark mottles are consistent with Beckers' (1968) spicule model.