Hypothesis testing on the planktic foraminiferal survival model after the KPB mass extinction: evidence from Tunisia and Algeria

A historical review of the extinction, survival, and evolutionary models of planktic foraminifera proposed for the Cretaceous/Paleogene boundary (KPB) mass extinction event sometimes leaves the impression that there is still no conclusive evidence to support any single one of them. Two main models have been put forward: i) catastrophic mass extinction, almost total for some authors, compatible with the geologically instantaneous paleoenvironmental effects of a large meteorite impact (Chicxulub impact, Mexico); and ii) gradual mass extinction, compatible with the paleoenvironmental effects of massive, long-lasting volcanism (Deccan Traps, India). Over the years, a lot of evidence has been proposed supporting one hypothesis or the other, highlighting isotopic (delta O-18, delta C-13, Sr-87/Sr-86) as well as taphonomic, biostratigraphic, quantitative (relative and/or absolute abundance), phylogenetic, and even teratological. We review previous planktic foraminiferal and stable isotope studies, and provide new quantitative and statistical tests from two pelagic sections: the El Kef section (Tunisia), recognized as the most continuous and expanded lowermost Danian section worldwide, and the Sidi Ziane section (Algeria), affected by relevant hiatus in the lower Danian. The results indicate that all the latest Maastrichtian planktic foraminiferal species except those of Guembelitria went extinct exactly at the KPB, supporting the hypothesis of an almost total extinction. In the light of this new evidence, we maintain that the Maastrichtian planktic foraminiferal specimens found worldwide in lower Danian samples could be the result of similar reworking and vertical mixing processes to those at El Kef and Sidi Ziane

Mineralogical Study of a White Clast from Murchison (CM2): Comparison with R-Chondrites

R-chondrites share some properties with ordinary chondrites (OC) and carbonaceous chondrites (CC). The proportions of the textural types of chondrule from R chondrites and their FeO/(FeO+MgO) ratios are similar to those of OC, but the high matrix abundance in R chondrites more closely resembles that of CC (matrix abundances: OC ~12 vol% vs. CC 34->60 vol%;). In this study, we characteristize the mineralogy of a white clast from Murchison (CM2), which was earlier considered to be a R-chondrite. First, all the petrographic and mineralogical characteristics will be described and compared with those of R-chondrites. Finally, all data will be considered in order to test, whether this clast is a real R-chondrite or a unique recrystallized chondrite

A Re-Investigation of a Chondritic Xenolith in the Murchsion (CM2) Chondrite: Formation by Fluid-Assisted Percolation During Metamorphism

The CM chondrites are generally complex impact breccias, in which lithic clasts and mineral fragments showing various degrees of aqueous alteration and possibly originating from different parent bodies are mixed together. The occurrence of CM-like clasts in other chondritic and achondritic meteorite breccias is also well-documented, however, reports on the occurrence of foreign clasts in CM chondrites are rare. In this study, we reinvestigated the white clast in the Murchison CM chondrite and demonstrate that the clast is not related to R chondrites as earlier suggested. In addition to the classification we discuss the origin and the history of its formation by studying several aspects like mineralogy, bulk chemistry, Rare Earth Elements (REE), oxygen isotopes, and the soluble organic compounds

Absolute Electron Emission Calibration: Round Robin Tests of Au and Polyimide

Accurate determination of the absolute electron yields of conducting and insulating materials are essential for models of spacecraft charging and related processes involving charge accumulation and emission due to electron beams and plasmas. Apparatus using low-fluence pulsed electron beam sources and various methods to minimize charge accumulation have been developed at facilities around the world. This study presents a round robin comparison of such tests performed in CSIC at Instituto de Ciencia de Materiales de Madrid, LaSeine at Kyushu Institute of Technology, DESSE at ONEREA, and the Space Environment Effects Materials (SEEM) test facility at Utah State University. The primary objectives of the study were to determine the consistency and uncertainties of these absolute yields measurements, and to investigate the effects of the similarities and differences of the diverse facilities. Measurements were made of the absolute total, secondary and backscattered electron yields at normal incidence over the full range of incident energies accessible with each group’s instrumentation (a full range of ~5 eV to ~30 keV). Electron emission spectra at specific incident electron energies were also measured. Measurements were made for identical samples with reproducible sample preparation of two standard materials: (1) the elemental conductor Au (25 μm thick 6N high purity Au foils) and (2) the polymeric insulator polyimide (25 μm thick Kapton HNTM). Studies of the effects on electron yield of Au surface contamination—as measured with Auger Electron Spectroscopy and other techniques—were made for samples: (1) as received, (2) subject to a simple standard cleaning procedure, (3) subsequently baked out under ultrahigh vacuum, and (4) after Ar ion sputter cleaning and thermal annealing. Similarly, studies of the effects of absorbed water and volatile compounds on electron yield were made for polyimide samples: (1) unbaked and (2) subjected to a vacuum bake out. An outline of measurement and analysis techniques used by each laboratory is presented, along with methods used to calibrate the incident energies and absolute yields measured with their different electron detectors. The effects of different charge minimization and neutralization methods are compared. Various empirical and physics-based models to characterize the electron yield curves are used to parameterize the yield data. The values determined at each laboratory for the maximum yield and energy at this yield, the first and second crossover energies, and the asymptotic yield at high energy are also compiled and compared

Les résidences fermées dans les périphéries d’Alger, produits d’un impératif sécuritaire et de disparités sociales

This research aims primarily to give persuasive highlights on the context causing the proliferation of closed and secure residences, in Algiers-city, and therefore to identify their specific characteristics. The insecurity and the political unrest incurred in Algeria, and in a particular way in Algiers and its suburbs areas, during a decade between 1988 and 1997 were mainly responsible of the development of these gated communities. However, the housing crisis and the important programs of property developers are at the origin of their significant evolution and their spread out to other prefectures of Algeria. Nowadays, living in luxurious residences is a sign of belonging to a certain social rank. These communities are often criticized for being an indication of rampant social segregation and sometimes carrier of germs of spatial inequality

Impact-generated carbonate melts in the Talemzane impact structure (Laghouat, Algeria)

International audienc

Assessement of flood hazards in eastern Mitidja Plain (Hamiz river and Reghaïa river) Algiers - Algeria

The Eastern Mitidja Plain, highly urbanized in its Northern part, is crossed by two main rivers: the Réghaïa and Hamiz wadis. Along these wadis, anarchical buildings are developing. An exceptional flood may weaken these zones. Flood hazard détermination needs a statistic analysis of daily maximum rainfalls, which adjustments to the Gumbel law allows to determinate the maximum rainfall for different return periods. The calculation of maximum discharges linked to différent return periods allows evaluating the overflowing on cross section along the Hamiz and Réghaïa wadis. Hazard maps, obtained for each wadis, evidence zones that are potentially threatened by flooding. Such maps should be considered and used as the main tools reduce the risk

Assessement of flood hazards in eastern Mitidja Plain (Hamiz river and Reghaïa river) Algiers - Algeria

The Eastern Mitidja Plain, highly urbanized in its Northern part, is crossed by two main rivers: the Réghaïa and Hamiz wadis. Along these wadis, anarchical buildings are developing. An exceptional flood may weaken these zones. Flood hazard détermination needs a statistic analysis of daily maximum rainfalls, which adjustments to the Gumbel law allows to determinate the maximum rainfall for different return periods. The calculation of maximum discharges linked to différent return periods allows evaluating the overflowing on cross section along the Hamiz and Réghaïa wadis. Hazard maps, obtained for each wadis, evidence zones that are potentially threatened by flooding. Such maps should be considered and used as the main tools reduce the risk