THE IMPACT-FLOOD CONNECTION: DOES IT EXIST?*

In a recent article in Terra Nova, Kristan-Tollmann and Tollmann (1994) suggested that the Biblical Flood can be explained by seven fragments of a comet that impacted the ocean at seven locations on Earth at 03.00h (C.E.T.) on 23 September, 9545 yr BP. We demonstrate that all the ‘geological proofs’ that allegedly support their conclusions are not supported by the available data on impact cratering. Their hypothesis is based on insufficient and ambiguous data, selective citation, and incomplete comprehension of previous research.     

The age of the Saltpan impact crater,South Africa

Abstract— The 1.13-km-diameter Pretoria Saltpan impact crater is located about 40 km NNW of Pretoria, South Africa. The crater is situated in 2.05 Ga old Nebo granite of the Bushveld Complex that is locally intruded by about 1.3 Ga old volcanic rocks. In 1988, a borehole was drilled in the center of the crater. At depths >90 m, breccias were found that contained minerals with characteristic shock-metamorphic features, thus confirming the impact origin of the crater. Fragments of impact glass were recovered from the melt breccias and several hundred sub-millimeter-sized glass fragments were subjected to fission track analysis. The measurements were complicated by the inhomogeneous composition of the impact glasses, but analysis of a large number of tracks yielded an age of 220 ± 52 ka for the Saltpan crater.     

Close binary EHB stars from SPY

We present the results of a radial velocity (RV) survey of 46 subdwarf B (sdB) and 23 helium-rich subdwarf O (He-sdO) stars. We detected 18 (39%) new sdB binary systems, but only one (4%) He-sdO binary. Orbital parameters of nine sdB and sdO binaries, derived from follow-up spectroscopy, are presented. Our results are compared with evolutionary scenarios and previous observational investigations.     

Shock metamorphism of quartz in nature and experiment: II. Significance in geoscience*

Abstract— The occurrence of shock metamorphosed quartz is the most common petrographic criterion for the identification of terrestrial impact structures and lithologies. Its utility is due to its almost ubiquitous occurrence in terrestrial rocks, its overall stability and the fact that a variety of shock metamorphic effects, occurring over a range of shock pressures, have been well documented. These shock effects have been generally duplicated in shock recovery experiments and, thus, serve as shock pressure barometers. After reviewing the general character of shock effects in quartz, the differences between experimental and natural shock events and their potential effects on the shock metamorphism of quartz are explored. The short pulse lengths in experiments may account for the difficulty in synthesizing the high-pressure polymorphs, coesite and stishovite, compared to natural occurrences. In addition, post-shock thermal effects are possible in natural events, which can affect shock altered physical properties, such as refractive index, and cause annealing of shock damage and recrystallization. The orientations of planar microstructures, however, are unaffected by post-impact thermal events, except if quartz is recrystallized, and provide the best natural shock barometer in terms of utility and occurrence. The nature of planar microstructures, particularly planar deformation features (PDFs), is discussed in some detail and a scheme of variations in orientations with shock pressure is provided. The effect of post-impact events on PDFs is generally limited to annealing of the original glass lamellae to produce decorated PDFs, resulting from the exsolution of dissolved water during recrystallization. Basal (0001) PDFs differ from other PDF orientations in that they are multiple, mechanical Brazil twins, which are difficult to detect if not partially annealed and decorated. The occurrence and significance of shock metamorphosed quartz and its other phases (namely, coesite, stishovite, diaplectic glass and lechatelierite) are discussed for terrestrial impact structures in both crystalline (non-porous) and sedimentary (porous) targets. The bulk of past studies have dealt with crystalline targets, where variations in recorded shock pressure in quartz have been used to constrain aspects of the cratering process and to estimate crater dimensions at eroded structures. In sedimentary targets, the effect of pore space results in an inhomogeneous distribution in recorded shock pressure and temperature, which requires a different classification scheme for the variation of recorded shock compared to that in crystalline targets. This is discussed, along with examples of variations in the relative abundances of planar microstructures and their orientations, which are attributed to textural variations in sedimentary target rocks. Examples of the shock metamorphism of quartz in distal ejecta, such as at the K/T boundary, and from nuclear explosions are illustrated and are equivalent to that of known impact structures, except with respect to characteristics that are due to long-term, post-shock thermal effects. Finally, the differences between the deformation and phase transformation of quartz by shock and by endogenic, tectonic and volcanic processes are discussed. We confirm previous conclusions that they are completely dissimilar in character, due to the vastly different physical conditions and time scales typical for shock events, compared to tectonic and volcanic events. Well-characterized and documented shock effects in quartz are unequivocal indicators of impact in the natural environment.     

Spectroscopic analysis of sdB stars from the ESO Supernova Ia Progenitor Survey

We report on the analysis of high-resolution optical spectra for 77 subdwarf B (sdB) stars from the ESO Supernova Ia Progenitor Survey. Effective temperature, surface gravity, and photospheric helium abundance are determined simultaneously by spectral line profile fitting of hydrogen and helium lines, and are found to be in agreement with previous studies of sdB stars. Twenty four objects show spectral signs of a cool companion, being either companion absorption lines or a flux contribution at Hα. Five stars with relatively high luminosity show peculiar Hα profiles, possibly indicating stellar winds. Our results are compared to recent theoretical simulations by Han et al. [MNRAS, 341, 669] for the distribution in effective temperature and surface gravity, and are found to agree very well with these calculations. Finally, we present a binary system consisting of two helium-rich hot subdwarfs.     

Literal solution for Hill's lunar problem

A computer program for the manipulation of power series in several variables is used to find the first order solution to Hill's lunar problem. The ratiom of the mean motion of the Sun to that of the Moon is kept as a formal parameter. The series inm are known to converge very poorly. It is shown how efficient algorithms among them the Lie transformation allow us to compute the series inm as far as they are needed. When the series are evaluated at Brown's numerical value form the results achieve or exceed his accuracy.     

Exact Brans-Dicke-Bianchi types-II,VIII, and IX stiff matter solutions

Exact solutions of the Brans-Dicke field equations of Bianchi types-II, VIII, and IX are derived. The solutions represent locally rotationally symmetric universes with stiff matter content.