Eruptive history of the Barombi Mbo Maar, Cameroon Volcanic Line, Central Africa: Constraints from volcanic facies analysis     

Boris Chako Tchamabé  Dieudonné Youmen  Sébastien Owona  Issa  Takeshi Ohba  Károly Németh  Moussa Nsangou Ngapna  Asobo N. E. Asaah  Festus T. Aka  Gregory Tanyileke  Joseph V. Hell 《Central European Journal of Geosciences》2013,5(4):480-496

his study presents the first and detail field investigations of exposed deposits at proximal sections of the Barombi Mbo Maar (BMM), NE Mt Cameroon, with the aim of documenting its past activity, providing insight on the stratigraphic distribution, depositional process, and evolution of the eruptive sequences during its formation. Field evidence reveals that the BMM deposit is about 126m thick, of which about 20m is buried lowermost under the lake level and covered by vegetation. Based on variation in pyroclastic facies within the deposit, it can be divided into three main stratigraphic units: U₁, U₂ and U₃. Interpretation of these features indicates that U₁ consists of alternating lapilli-ash-lapilli beds series, in which fallout derived individual lapilli-rich beds are demarcated by surges deposits made up of thin, fine-grained and consolidated ash-beds that are well-defined, well-sorted and laterally continuous in outcrop scale. U₂, a pyroclastic fall-derived unit, shows crudely lenticular stratified scoriaceous layers, in which many fluidal and spindle bombs-rich lapilli-beds are separated by very thin, coarse-vesiculatedash-beds, overlain by a mantle xenolith- and accidental lithic-rich explosive breccia, and massive lapilli tuff and lapillistone. U3 displays a series of surges and pyroclastic fall layers. Emplacement processes were largely controlled by fallout deposition and turbulent diluted pyroclastic density currents under “dry” and “wet” conditions. The eruptive activity evolved in a series of initial phreatic eruptions, which gradually became phreatomagmatic, followed by a phreato-Strombolian and a violent phreatomagmatic fragmentation. A relatively long-time break, demonstrated by a paleosol between U₂ and U₃, would have permitted the feeding of the root zone or the prominent crater by the water that sustained the next eruptive episode, dominated by subsequent phreatomagmatic eruptions. These preliminary results require complementary studies, such as geochemistry, for a better understanding of the changes in the eruptive styles, and to develop more constraints on the maar’s polygenetic origin.  相似文献   

Organisation hydrochimique,biologique et sédimentologique d’un lac intracontinental à peuplements lagunaires : la Birket Karoun (Fayoum,Egypte)     

Jean-Pierre Perthuisot  Olivier Guelorget  Ahmed Wahid et Sayed Ibrahim  Jean-Pierre Margerel  André Maurin  Maryvonne Piron-Frenet 《Geodinamica Acta》2013,26(2):73-89

Résumé

La Birket Karoun a été étudiée d’un point de vue biogéologique sur une période de 12 mois. Les données ainsi obtenues, ajoutées à celles de la littérature disponible, permettent de présenter les caractéristiques biogéologiques essentielles de ce bassin original.

Le lac n’est alimenté actuellement que par des eaux continentales issues du système nilotique ce qui entraîne des propriétés hydrochimiques assez différentes des corps d’eau paraliques influencés par la mer. Cependant, les caractéristiques hydrologiques, biologiques et sédimen-taires de la Birket Karoun la classent parmi les écosystèmes de type lagunaire. Il est même possible d’y reconnaître une organisation biogéologique zonale très semblable à celle des lagunes, la partie la plus « marine » (ou la moins confinée) se situant à l’opposé de la zone des apports d’eau douce. Une connexion entre le lac et la mer, actuelle ou passée, étant à peu près exclues, il faut admettre que les eaux continentales concentrées peuvent présenter, dans certains cas, des caractéristiques chimiques et biochimiques presque marines vis-à-vis des êtres vivants.

Dans cette optique, la Birket Karoun apparaît comme un modèle actuel susceptible de fournir une alternative à l’hypothèse d’une « Mer Saharienne » pour rendre compte de l’existence des lacs sahariens pleistocènes à faunes fossiles lagunaires.  相似文献   

Late Cretaceous ophiolite obduction and Paleocene India-Asia collision in the westernmost Himalaya     

Richard A. Beck  Douglas W. Burbank  William J. Sercombe  Asrar M. Khan  Robert D. Lawrence 《Geodinamica Acta》2013,26(2-3):114-144

Abstract

Collision of the Kohistan island arc with Asia at ~100 Ma resulted in N-S compression within the Neo-Tethys at a spreading center north of the Indo-Pakistani craton. Subsequent India-Asia convergence converted the Neo-Tethyan spreading center into a short-lived subduction zone. The hanging wall of the subduction zone became the Waziristan, Khost and Jalalabad igneous complexes. During the Santonian- Campanian (late Cretaceous), thrusting of the NW IndoPakistani craton beneath Albian oceanic crust and a Cenomanian volcano-sedimentary complex, generated an ophiolite-radiolarite belt. Ophiolite obduction resulted in tectonic loading and flexural subsidence of the NW Indian margin and sub-CCD deposition of shelf-derived olistostromes and turbidites in the foredeep. Campanian-Maastriehtian calci- clastic and siliciclastic sediment gravity flows derived from both margins filled the foredeep as a huge allochthon of Triassic-Jurassic rise and slope strata was thrust ahead of the ophiolites onto the Indo-Pakistani craton. Shallow to intermediate marine strata covered the foredeep during the late Maastrichtian. As ophiolite obduction neared completion during the Maastrichtian, the majority of India-Asia convergence was accommodated along the southern margin of Asia. During the Paleocene, India was thrust beneath a second allochthon that included open marine middle Maastrichtian colored mélange which represents the Asian Makran-Indus-Tsangpo accretionary prism. Latérites that formed on the eroded ophiolites and structurally higher colored mélange during the Paleocene wei’e unconformably overlapped by upper Paleocene and Middle Eocene shallow marine limestone and shale that delineate distinct episodes of Paleocene collisional and Early Eocene post-collisional deformation.  相似文献   

Seasonal changes in zooplanktonic alkaline phosphatase activity in Toulon Bay (France): the role of Cypris larvae     

Jean N  Bogé G  Jamet JL  Richard S  Jamet D 《Marine pollution bulletin》2003,46(3):346-352

We studied zooplankton contribution to the total particulate phosphatase activity, the kinetics of this activity, the relation to the different taxonomic groups and the role of particle-bound bacteria. The activity of total particulate material collected from a liter of seawater was more elevated in May, June and August than during the rest of the year. These high activities resulted from a high contribution of the >90 microm fraction which account then for more than 60% of the total particulate activity. Two Michaelian processes with high and low V(max) were disclosed on this fraction. The high V(max) component was responsible for the high summer activities. During these periods, high densities of cirriped Cypris were found which were statistically correlated with this high V(max) component as with its specific activity. Moreover, the contribution of attached bacteria to these high activities was low. In return, this contribution was predominant during the periods of low activity. A simple method was developed to characterise this bacterial activity.  相似文献   

Reionization and the Cosmic Dawn with the Square Kilometre Array     

Garrelt Mellema  Léon V. E. Koopmans  Filipe A. Abdalla  Gianni Bernardi  Benedetta Ciardi  Soobash Daiboo  A. G. de Bruyn  Kanan K. Datta  Heino Falcke  Andrea Ferrara  Ilian T. Iliev  Fabio Iocco  Vibor Jelić  Hannes Jensen  Ronniy Joseph  Panos Labroupoulos  Avery Meiksin  Andrei Mesinger  André R. Offringa  V. N. Pandey  Jonathan R. Pritchard  Mario G. Santos  Dominik J. Schwarz  Benoit Semelin  Harish Vedantham  Sarod Yatawatta  Saleem Zaroubi 《Experimental Astronomy》2013,36(1-2):235-318

The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21 cm line from the earliest phases of star and galaxy formation in the Universe. This 21 cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope.  相似文献   

Towards an operational system for oil-spill forecast over Spanish waters: initial developments and implementation test     

Sotillo MG  Fanjul EA  Castanedo S  Abascal AJ  Menendez J  Emelianov M  Olivella R  García-Ladona E  Ruiz-Villarreal M  Conde J  Gómez M  Conde P  Gutierrez AD  Medina R 《Marine pollution bulletin》2008,56(4):686-703

The ESEOO Project, launched after the Prestige crisis, has boosted operational oceanography capacities in Spain, creating new operational oceanographic services and increasing synergies between these new operational tools and already existing systems. In consequence, the present preparedness to face an oil-spill crisis is enhanced, significantly improving the operational response regarding ocean, meteorological and oil-spill monitoring and forecasting. A key aspect of this progress has been the agreement between the scientific community and the Spanish Search and Rescue Institution (SASEMAR), significantly favoured within the ESEOO framework. Important achievements of this collaboration are: (1) the design of protocols that at the crisis time provide operational state-of-the-art information, derived from both forecasting and observing systems; (2) the establishment, in case of oil-spill crisis, of a new specialized unit, named USyP, to monitor and forecast the marine oceanographic situation, providing the required met-ocean and oil-spill information for the crisis managers. The oil-spill crisis scenario simulated during the international search and rescue Exercise "Gijón-2006", organized by SASEMAR, represented an excellent opportunity to test the capabilities and the effectiveness of this USyP unit, as well as the protocols established to analyze and transfer information. The results presented in this work illustrate the effectiveness of the operational approach, and constitute an encouraging and improved base to face oil-spill crisis.  相似文献   

Effects of the 'Prestige' oil spill on macroalgal assemblages: large-scale comparison     

Lobón CM  Fernández C  Arrontes J  Rico JM  Acuña JL  Anadón R  Monteoliva JA 《Marine pollution bulletin》2008,56(6):1192-1200

An assessment of the effects of the 'Prestige' oil spill on intertidal, macroalgal assemblages was carried out comparing abundance data obtained before and after the spill. Four zones in the North and Northwest coast of Spain were sampled, one of them located at the immediate vicinity of the spill, the zone most heavily oiled. Macroalgal assemblages had similar structure between years. Neither critical decrease in abundance of the dominant macroalgae, nor increase in opportunistic species were found. Some differences in abundance were observed, but they did not show any pattern, being more likely the result of the natural variability of the assemblage. Extensive, but not intense fuel deposition on the shores and a limited use of aggressive cleanup methods are suggested as possible causes for the lack of the effects in these assemblages after the 'Prestige' oil spill.  相似文献   

Methodology of seasonal morphological modelisation for nourishment strategies on a Mediterranean beach     

Larroudé P 《Marine pollution bulletin》2008,57(1-5):47-52

A modified 2DH morphodynamical model was employed to simulate the evolution of large-scale features with major implications for beach nourishment. The study was focused on modelling the evolution of material artificially placed in different parts of the profile, extracting or adding material to the natural bars, and quantifying how the profile responds to different wave climates and nourishment placements. The simulated results were compared with field data from a Mediterranean beach.  相似文献   

Organochlorine pesticide levels in loggerhead turtles (Caretta caretta) stranded in the Canary Islands, Spain     

Monagas P  Orós J  Araña J  González-Díaz OM 《Marine pollution bulletin》2008,56(11):1949-1952

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Multivariate discriminant analysis distinguishes metal- from non metal-related biomarker responses in the clam Chamaelea gallina     

Rodríguez-Ortega MJ  Rodríguez-Ariza A  Gómez-Ariza JL  Muñoz-Serrano A  López-Barea J 《Marine pollution bulletin》2009,58(1):64-327

Molecular biomarkers are among the most sensitive and earliest responses to pollutants. However, lack of detailed knowledge on variability of responses and their possible seasonal variation limit their use. In addition, the seasonality of biological processes modulates the response of organisms to pollutant stressors. Using multivariate statistics, we have studied the influence of environmental and biological factors on the response of a battery of molecular biomarkers in the clam Chamaelea gallina collected along the South-Spanish littoral. Multivariate discriminant analysis clearly distinguished biomarker response between clean and polluted areas, using heavy metals as indicator of pollution. Such differences disappeared when the dataset was normalised for metal content, thus indicating that pollution was the main significant cause of the changes observed between clean and polluted sites. In conclusion, this work shows that, when applying a complete biomarker panel, multivariate statistical tools can be used to discern pollutant- from non pollutant-related responses.  相似文献