Notes sur la Géochimie du Pétrole

Résumé L'altération naturelle d'un pétrole de base mixte des couches de Péchelbronn et d'un pétrole de base paraffinique de Staffelfelden produit un asphalte de base naphténique. Dans le fossé rhénan il existe un groupe d'huiles brutes mixtes dans les formations post-jurassiques et un groupe de pétroles paraffiniques dans les formations antejurassiques.     

Correction to: A Deep-Learning-Based Geological Parameterization for History Matching Complex Models

Mathematical Geosciences - In the original paper, the units noted on the x-axes in Fig. 17a and b are incorrect.     

Estimation of spawning habitats of market squid (Doryteuthis opalescens) from field surveys of eggs off Central and Southern California

Like many other loliginid squid, Doryteuthis (Loligo) opalescens deposits egg cases on the ocean floor. Depending upon temperature, egg cases may persist for 5–12 weeks before the paralarvae hatch. Because of this relatively long duration and squid’s pelagic life history, egg cases provide a practical life stage to survey. During 2001–2002, squid egg beds in Monterey Bay, Carmel Bay, and around the California Channel Islands were surveyed using a remotely operated vehicle with the goal of delineating the habitat of egg beds that are spawned during active commercial fishing. Egg cases were highly aggregated and densities reached 1338 capsules m⁻². Squid eggs were significantly shallower in Central California. Egg cases occurred between 20 and 93 m around the Channel Islands, and in Central California they were between 13 and 61 m. The temperatures in both regions were similar (10–12 °C), with some eggs in Southern California found up to 14.4 °C. Ninety-five percent of eggs were found on sand, suggesting that temperature and substrate are stronger behavioral cues than depth to stimulate spawning. Suitable spawning habitat was defined by three criteria: sandy benthic substrate, temperatures between 10 and 14.4 °C, and depths between 20 and 70 m when the first two criteria hold. Additionally, within this defined area, oxygen concentration is quantified. The greatest commercial landings of market squid occur in both Central and Southern California during a time of year when water temperatures of 10–12 °C are prevalent in the 20–70 m depth range.     

Mechanisms of lateral and linear extension of gullies (dongas) in a subhumid grassland of South Africa

The formation of deep gullies (called ‘dongas’ locally) in rangeland in KwaZulu-Natal Province in South Africa is a natural phenomenon. These U-shaped, very wide gullies have considerable lateral expansion due to the episodic collapse of sidewalls. The dongas have developed in duplex soils such as Luvisols and Lixisols formed on Permian sedimentary rocks or unconsolidated Quaternary colluvium. This study combined morphological, mineralogical and chemical characterization with measurements of grain-size content, structural stability and the complete shrinkage curve to detect changes in soil properties of the different horizons located in the gully banks. The different soil horizons present clear and sharp differences in physical and mineralogical properties. The topsoil with complete grass cover is very resistant to soil detachment. However, the leached E horizon and the BC horizon have low structural stability. The soil profile down to and including the Bt horizon contains exclusively illite in the clay fraction, while the BC colluvial layer and the C horizon (mudstone) contain expandable interstratified illite–smectite. The Bt horizon has a high water content at saturation and high shrinkage, while the BC and C horizons have a high residual shrinkage and a very low water content at saturation. Because this type of gully expansion is not significantly linked to slope value or the stream power index (SPI) at the gully head, to land-use change, high rainfall intensities or the threshold of concentrated runoff being exceeded at the gully head, other causes were investigated. It was concluded that the heterogeneity between horizons with different mineralogical properties and structural stabilities, soil types and parent material, anisotropic water-saturation and shrink-swell properties are of major importance. This heterogeneity between different soil horizon morphologies and their physical properties can explain why the relationship between the critical slope and the drainage area for gully initiation showed a threshold for gullying much lower than that found elsewhere. © 2020 John Wiley & Sons, Ltd.     

法国、中国断陷盆地厚煤层堆积机制分析

从法国中央地块晚石炭世的3个内陆山间小型断陷聚煤盆地厚煤层的成因标志和沉积特征出发,讨论了这些煤层独特的堆积机制及其沉积-构造条件,并与中国东北早第三纪抚顺盆地超厚煤层的沉积条件做了比较分析,指出了2个大陆间在厚煤层的堆积背景与条件方面的差异性和共同点。尤其是这些盆地均发育于活动的构造背景之下,盆缘、盆内断层活动强烈,且控制着沉积相带的展布及富煤单元的时空分布;煤层内均发育有大量的重力流沉积物——碎屑流。稀性泥石流或浊流沉积物;煤层自身存在同沉积期的重力滑塌。变形构造和大量的再搬运-再堆积的记录,表明厚（巨厚、超厚）煤层在堆积时的湖泊环境为覆水较深、不稳定的沉积环境,并且煤（泥炭）在初次堆积后经过了再次搬运而成为异地堆积的产物。这为提出厚煤层新的堆积机制,即异地堆积提供了重要而可靠的证据和实例。     

Twentieth century changes in montane vegetation in the eastern Free State,South Africa,derived from palynology of hyrax dung middens

The dating and pollen analysis of a hyrax dung deposit in a mountain rock shelter (Rooiberg Shelter II) are compared with that in a previous study from the same mountain range at the rural town Clarens, in South Africa. Calibration of radiocarbon measurements from the dung deposit provides different possibilities for the age of the sequence. Unlikely dates can be eliminated on the basis of pollen stratigraphy, comparisons with a previously studied accumulation from the last 30 yr, artificially increased radiocarbon levels in the upper samples as result of nuclear arms testing after 1954, the presence of historically introduced exotic elements, and the assumption of a relatively constant rate of dung accumulation. According to these considerations we suggest that the dung started accumulating at the beginning of the twentieth century. The pollen contents show marked changes in composition, indicating mainly open grass vegetation with fynbos in the first half of this century and woody vegetation in the second half. A first marked increase of the woody component is estimated to have occurred around 1950, but it only became permanent in the 1960s. The fluctuating pollen sequence can best be interpreted in terms of the combined effects of rainfall changes, fire and stock grazing, the latter of which increased together with town expansion in the area during the course of this century. Considering historical events recorded in the area and the region in general, the results suggest that pollen in hyrax dung is a good recorder of vegetation change. Copyright © 1999 John Wiley & Sons, Ltd.