Nom du corpus

Corpus Systématique Végétale

Titre du document

Diatoms for reconstructing palaeoenvironments and paleohydrology in tropical semi-arid zones

Lien vers le document
Éditeur
Springer (journals)
Langue(s) du document
Anglais
Type de document
Research-article
Mots-clés d'auteur
  • diatoms
  • palaeolimnology
  • tropical Africa
  • Holocene
Nom du fichier dans la ressource
Syst_veg6_v2_012303
Auteur(s)
  • F. Gasse
Affiliation(s)
  • Ecole Normale Supérieure, BP 81, F-92266, Fontenay-aux-Roses Cedex
  • Université Paris-Sud, UA 723, CNRS, Bât. 504, F-91405, Orsay Cedex, France
Résumé

Palaeoenvironments are reconstructed from the diatom flora of Holocene swamp and lacustrine sediments which lie in closed depressions of the Chad basin (Niger). The geological and hydrological setting of the sedimentary profiles investigated is presented in section I. Three types of hydrological environments are considered: depressions which have been connected with L. Chad during the Holocene, small river-fed basins outside of the maximum extension of L. Chad, and depressions which have been mainly supplied by groundwater. Methods used for palaeoecological reconstruction are discussed (section II) on the basis of the present-day distribution of diatom species and communities in the investigated zones. Attention is drawn to the diversity of the habitats in a given waterbody, and on the potential effects of seasonality and water stratification on the composition of diatom assemblages contained in the sediments. Because of the spatial and temporal changes in diatom communities, the sediment may integrate a mixture of communities with different ecological requirements. Thus, mean values of individual ecological variables deduced from a fossil assemblage are not sufficient to characterize a palaeoenvironment. In section III, a classification of the palaeoenvironments is proposed. One attempts to distinguish the different communities contained in the fossil assemblages. The fossil communities are compared to diatom populations living today in the studied zones, or in other African sectors when no regional analogue has been found, and for which ecological conditions are known. This allows environmental characteristics to be inferred from sedimentary profiles. At a given time, the palaeosystems show the same ecological diversity as the modern ones. The main status of the palaeoenvironmental evolution are then drawn for each stratigraphical profile (section IV), for an understanding of their causes. The major climatic tendancies affecting intertropical Africa have been chiefly responsible for the presence or absence of aquatic environments in the closed depressions. Superimposed to that, the diversity and the evolution of the individual palaeoecosystems have been controlled by local topographical and hydrological factors (origin of water, permeability of lake floor. . ). This is a common situation for waterbodies lying in tropical arid and semi-arid zones, and especially for palaeolakes associated to groundwater circulations. Therefore, palaeolimnological data can hardly serve as direct and accurate climatic indicators, if they are not corrected for the effects of local hydrology.

Catégories Science-Metrix
  • 1 - natural sciences
  • 2 - biology
  • 3 - marine biology & hydrobiology
Catégories INIST
  • 1 - sciences appliquees, technologies et medecines
  • 2 - sciences biologiques et medicales
  • 3 - sciences biologiques fondamentales et appliquees. psychologie
Catégories Scopus
  • 1 - Life Sciences ; 2 - Agricultural and Biological Sciences ; 3 - Aquatic Science
Catégories WoS
  • 1 - science ; 2 - marine & freshwater biology
Identifiant ISTEX
5CD73C0F590D3A6FCB06401A455658D18B5A1DC7
Revue

Hydrobiologia

Année de publication
1987
Présence de XML structuré
Non
Score qualité du texte
10
Version PDF
1.3
Type de publication
Journal
ark:/67375/1BB-0R6QTDZW-X
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