Evolution of the Nile deep‐sea turbidite system during the Late Quaternary: influence of climate change on fan sedimentation

This paper presents an overview of the evolution of the Nile deep‐sea turbidite system during the last 200 kyr, over a series of glacial to interglacial cycles. Six individual deep‐sea fans were identified from an extensive field data set. Each fan comprises a canyon, channel system and terminal lobes. Two of these fan systems were possibly active at the same time, at least during some periods. Large‐scale slope failures destroyed channel segments and caused the formation of new submarine fan systems. These slope failures thus played an important role in the overall evolution of the turbidite system. During the last glacial maximum (ca 25 to 14·8 ka) the central and eastern parts of the Nile deep‐sea turbidite system were relatively inactive. This inactivity corresponds to a lowstand in sea‐level, and a period of arid climate and relatively low sediment discharge from the Nile fluvial system. Rapid accumulation of fluvial flood‐derived deposits occurred across the shallower part of the submarine delta during sea‐level rise between ca 14·8 and 5 ka. The most recent deep‐sea channel–lobe system was very active during this period of rising sea‐level, which is also associated with a wetter continental climate and increased sediment and water discharge from the Nile. Increased sediment deposition in shallower water areas led to occasional large‐scale slope failure. The Nile deep‐sea turbidite system was largely inactive after ca 5 ka. This widespread inactivity is due to retreat of the coastline away from the continental shelf break, and to a more arid continental climate and reduced discharge of sediment from the Nile. The Nile deep‐sea turbidite system may be more active during periods of rising and high sea‐level associated with wetter climates, than during lowstands, and may rapidly become largely inactive during highstands in sea‐level coupled with arid periods. These acute responses to climate change have produced sedimentary/stratigraphic features that diverge from traditional sequence models in their nature and timing. This large‐scale sedimentary system responded to monsoon‐driven climate change and sea‐level change in a system‐wide and contemporaneous manner.     

The Trojan problem

There has been a renewed interest in the Trojan problem in recent years. Significant progress has been made in discovering and understanding dynamical features of motion of Jupiter's Trojan asteroids. The dynamics of hypothetical Trojan-type asteroids of other major planets has also been the subject of several recent investigations. This paper offers an overview on the current status of researches on real and hypothetical Trojan asteroids of the major planets. Results of analytical and numerical works are surveyed. Questions of dynamical properties, long-term evolution of orbits, stability regions around the triangular Lagrangian points are discussed among other problems of the Trojans.     

The motion of the perihelion of Trojan asteroids

The problem is investigated by using the equations of Jupiter's main perturbations in the eccentricity and in the perihelion longitude of Trojan asteroids. The limits and the period of the variation of the eccentricity and of the perihelion longitude are calculated for 30 Trojans. The perihelion is shown to circulate in 20 cases and to librate for 10 asteroids.     

Variabilité spatiale du signal palynologique dans le bassin de Paris à la limite Dogger–Malm

The drilling of new cores performed for ANDRA in eastern France allowed us to compare palynological data between central and eastern parts of the Paris Basin. Such a comparison, which was also motivated by the existence of a set of geochemical data in contradiction with the first palynological results, showed a spatial differentiation in palynological record from the Oxfordian. Such a palynological signal could result from overlapping of both local and global signals, the latter being in connection with the contemporaneous opening of proto-Atlantic Ocean. It could also be of major palaeogeographic and palaeoclimatic interest. To cite this article: V. Huault et al., C. R. Geoscience 335 (2003).